Catalytic alkane conversion

ABSTRACT

Disclosed is a hydrocarbon conversion process in which an alkane component is catalytically converted in the presence of an oxygen or oxidizing component (i.e., oxidant). The hydrocarbon conversion process can be an oxidative coupling reaction, which refers to the catalytic conversion of alkane in the presence of oxidant to produce an olefin product, i.e., a composition containing C2+ olefin. Reverse-flow reactors can be used to carry out the oxidative coupling reaction.

CROSS REFERENCE TO RELATED APPLICATIONS

Priority

This application is a divisional of U.S. patent application Ser. No.14/469,109, filed Aug. 26, 2014, and issued Jul. 12, 2016 as U.S. Pat.No. 9,388,094, which claims priority to and the benefit of (i) U.S.Provisional Patent Application No. 61/872,175, filed Aug. 30, 2013; (ii)E.P. Patent Application No. 12189746.4, filed Oct. 22, 2013; thecontents of which are incorporated herein by reference in theirentireties. Related: the following related cases are also incorporatedby reference in their entireties: (i) P.C.T. Application No.PCT/US2014/052710, filed Aug. 26, 2014, (ii) U.S. patent applicationSer. No. 14/469,141, filed Aug. 26, 2014; (iii) P.C.T. Application No.PCT/US2014/052715, filed Aug. 26, 2014; (iv) U.S. patent applicationSer. No. 14/469,180, filed Aug. 26, 2014; (v) P.C.T. Patent ApplicationNo. PCT/US2014/052722, filed Aug. 26, 2014; (vi) U.S. patent applicationSer. No. 14/469,227, filed Aug. 26, 2014; and (vii) P.C.T. PatentApplication No. PCT/US2014/052698, filed Aug. 26, 2014.

FIELD OF THE INVENTION

The invention relates to processes for catalytically converting alkane.The invention further relates to processes for catalytically convertingalkane to produce C₂₊ unsaturates, and to equipment useful in suchprocesses.

BACKGROUND OF THE INVENTION

Producing ethylene by methane dehydrogenation is an energy-intensivereaction. Since the reaction is endothermic and reaction temperaturesgreater than 800° C. are generally required to achieve practical methaneconversion levels, a significant amount of heat is required to maintainthe reaction. Generating this heat and transferring it to the methane isa significant cost, and can introduce inefficiencies into the process.In order to overcome some of these difficulties, there has beenconsiderable effort directed toward methane conversion via catalyticoxidative coupling reactions.

One process for producing ethylene from methane by catalytic oxidativecoupling is disclosed in Synthesis of Ethylene via Oxidative Coupling ofMethane, G. E. Keller and M. H. Bhasin, Journal of Catalysis 73, 9-19(1982). Although an appreciable selectivity to ethylene was observed (toa maximum of about 50%), conversion was relatively low. In order toovercome the methane-ethylene separation difficulties resulting from thelow methane conversion, technology has been developed for quenching thereaction product downstream of the oxidative coupling reactor, and thenseparating ethylene from the unreacted methane.

One process, disclosed in Enhanced C ₂ Yields from Methane OxidativeCoupling by Means of a Separative Chemical Reactor, A. E. Tonkovich, R.W. Carr, R. Aris, Science 262, 221-223, 1993, includes a simulatedcountercurrent moving-bed chromatographic reactor, and achieves 65%methane conversion and 80% selectivity to C₂ hydrocarbons. The reactoris configured in four sections, with each section comprising (i) acatalytic reactor containing Sm₂O₃ catalyst and (ii) an adsorbent columnlocated downstream of the catalytic reactor. Methane and oxygen reactvia catalytic oxidative coupling in the reactor at a temperature in therange of about 900° K to 1100° K, and then ethylene is separated fromunreacted methane in the sorption column. In order to maintainsufficient selectivity for ethylene sorption, the reactor's product isquenched to a temperature of 373° K in the sorption column. In anotherprocess, disclosed in Methane to Ethylene with 85 Percent Yield in a GasRecycle Electrocatalytic Reactor-Separator, Y. Jiang, I. V. Yentekakis,C. G. Vayenas, Science 264, 1563-1566, 1994, gas recycle is utilized tofurther increase methane conversion, but an even lower quenchtemperature (30° C.) is used during ethylene sorption.

Although the disclosed moving-bed and gas-recycle processes improveconversion, the quenching is energy intensive, and further improvementsare desired. Further improvements are particularly desired in convertingalkanes such as methane into C₂₊ olefins such as ethylene and propylene,particularly with increasing selectivity to ethylene production.

SUMMARY OF THE INVENTION

This invention provides a hydrocarbon conversion process that is lessenergy intensive than comparable processes. The hydrocarbon conversionprocess is particularly desirable for converting alkanes such as methaneinto C₂₊ olefins such as ethylene and propylene, especially withincreasing selectivity to ethylene production.

More particularly, the invention relates to a process for catalyticallyconverting alkane and oxidant to olefin. The process can be carried outin a flow-through reactor, e.g., a tube reactor. The flow-throughreactor comprises catalyst and at least one thermal mass. Hydrogencatalytically transfers from the alkane to the oxidant to produce areaction mixture, which is then quenched in the reactor by contactingthe reaction mixture with the thermal mass. The thermal mass is cooledafter the quenching. The process can be operated continuously byrepeating the catalytic transfer, quenching, and cooling steps. Olefincan be removed from the reaction mixture and/or quenched reactionmixture, e.g., by sorption. The removed olefin can be recovered bydesorption, e.g., for storage and/or further processing, such aspolymerization.

In certain aspects, the catalytic conversion is carried out in at leastone reverse-flow reactor. The reverse-flow reactor comprises catalyst, afirst thermal mass, and a second thermal mass. When operating thereverse-flow reactor in the forward direction, the first thermal mass,which has been preheated, transfers heat to alkane and oxidant in orderto (i) cool the first thermal mass and (ii) heat the alkane and oxidantto a temperature sufficient for catalytically reacting them to produce afirst reaction mixture. The first reaction mixture, which comprises C₂₊hydrocarbon produced by the reaction (e.g., olefin) and any unreactedfeed, transfer heat to the second thermal mass to (i) heat the secondthermal mass and (ii) cool the first reaction mixture. The flow ofalkane and oxidant is then reversed.

When operating the reverse-flow reactor in the reverse direction, thesecond thermal mass (which is heated when the reactor is operated in theforward direction) transfers heat to alkane and oxidant to (i) cool thesecond thermal mass and (ii) heat the alkane and oxidant to atemperature sufficient for catalytically reacting them to produce asecond reaction mixture. The second reaction mixture, which comprisesC₂₊ hydrocarbon produced by the reaction (e.g., olefin) and anyunreacted feed, transfers heat to the first thermal mass to (i) heat thefirst thermal mass and (ii) cool the second reaction mixture. Since thefirst thermal mass is now heated and the second thermal mass is nowcooled, the reverse-flow reactor is substantially restored to itsinitial condition. The flow of alkane and oxidant can be reversed again,in order to carry out the reaction in the forward direction. The processcan be operated continuously or semi-continuously, e.g., by alternatingthe flow direction of alkane and oxidant to the reverse-flow reactor,such as forward-flow, followed by reverse-flow, flowed by forward flow,followed by reverse-flow, etc.

Optionally, the reverse-flow reactor further comprises sorbent, e.g., atleast one sorbent for removing olefin from the first reaction mixturewhen the process is operated in the forward direction and/or at leastone sorbent for removing olefin from the second reaction mixture whenthe reactor is operated in the reverse direction. Optionally (i) thefirst thermal mass includes a first sorbent, or is itself, at least inpart, a first sorbent and/or (ii) the second thermal mass includes asecond sorbent, or is itself, at least in part, a second sorbent.Optionally, a plurality of reverse-flow reactors is utilized foroperating the process, the reactors being arranged in series, parallel,or series-parallel.

The process can further comprise, e.g., (i) removing olefin from thefirst reaction mixture with a second sorbent when the reverse-flowreactor is operated in the forward direction, and then desorbing fromthe second sorbent at least a portion of the removed olefin and (ii)removing olefin from the second reaction mixture with a first sorbentwhen the reverse-flow reactor is operated in the reverse direction, andthen desorbing from the first sorbent at least a portion of the removedolefin.

The reverse-flow reactor can comprise, e.g., first and second thermalmasses, each having first and second portions, the first and secondportions together comprising ≥99.0 wt. % of the first or second thermalmass as the case may be, wherein the first and thermal masses eachinclude one or more passages adapted for fluid flow. The reactor caninclude first, second, third, fourth, and fifth regions, wherein (i) thefirst and second regions are adjacent, non-overlapping regions, (ii) thethird and fourth regions are adjacent, non-overlapping regions, (iii)the first region contains the first portion of the first thermal massand the second region contains the second portion of the first thermalmass, (iv) the third region contains the first portion of the secondthermal mass and the fourth region contains the second portion of thesecond thermal mass, (v) the fifth region is a non-overlapping regionlocated between the second and third regions, and (vi) the fifth regionis adapted for distributing fluid between the first and second thermalmasses and optionally for fluid mixing. In order to react alkane andoxidant, e.g., in a forward direction, at least one first reaction zonecan be located in the second region, at least one of the reaction zonescontaining at least one first hydrocarbon conversion catalyst that is influid communication with the passage(s) of the first thermal mass. Atleast one first sorbent zone can be located in the first region, thefirst sorbent zone containing at least one olefin-selective sorbent thatis in fluid communication with the passage(s) of the first thermal mass.In order to react alkane and oxidant in a reverse direction, at leastone second reaction zone located in the third region, at least one ofthe reaction zones containing at least one second hydrocarbon conversioncatalyst that is in fluid communication with the passage(s) of thesecond thermal mass. At least one second sorbent zone can be located inthe fourth region, the second sorbent zone containing at least oneolefin-selective sorbent that is in fluid communication with the secondthermal mass.

In other aspects, the invention relates to one or more flow-throughreactors. The reactors are suitable for carrying out the process of anyof the preceding aspects. In other aspects, the invention relates to asystem for converting alkane to C₂₊ olefin.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are simplified diagrammatic illustrations of certainprocess steps in a regenerative reverse-flow reactor system.

FIGS. 2A and 2B are simplified diagrammatic illustrations of certainprocess steps in a regenerative reverse-flow reactor system includingreaction and olefin sorption zones.

FIG. 3 is a simplified diagrammatic illustration of a two stagereverse-flow reactor utilized for converting a feed into conversionproducts containing olefins in accordance with certain aspects theinvention.

FIG. 4 is a simplified diagrammatic illustration of desorbing olefinfrom the two stage reverse-flow reactor in accordance with certainaspects the invention.

FIG. 5 is a simplified diagrammatic illustration of a reverse flow offeed through the two stage reverse-flow reactor in accordance withcertain aspects the invention.

Although the invention can be described in terms of a hydrocarbonconversion process, particularly an oxidative-transfer reaction process,for producing olefins such as ethylene and propylene, the invention isnot limited thereto. In other words, to the extent that the followingdetailed description is specific to a particular embodiment or aparticular use, this is intended to be illustrative only, and is not tobe construed as limiting the scope of the invention. On the contrary, itis intended to cover all alternatives, modifications and equivalentsthat may be included within the spirit and scope of the invention.

DETAILED DESCRIPTION OF THE INVENTION Definitions

For the purpose of this description and appended claims, the followingterms are defined.

The term “conduit” refers to means for conducting a composition from onelocation to another. The term conduit encompasses (i) elementaryconducting means, such as a pipe or tube and (ii) complex means such astortuous pathways through conducting means, e.g., pipes, tubes, valves,and reactors that are filled with random packing. One or more conduitsare typically utilized for conveying fluid into and through the thermalmass. A single conduit located in a thermal mass is a passage, and thethermal mass typically includes at least one passage. The term “passage”means a geometrically contiguous volume element that can be utilized forconveying a fluid within a reactor, regenerator, recuperator, reactorbed, regenerative bed, thermal mass, monolith, honeycomb, etc.Generally, the thermal mass contains at least one channel (arranged as aphysical and/or conceptual set or group of passages). The term “channel”means a plurality of passages that can be utilized together forconveying a fluid within the reactor, regenerator, recuperator,regenerative bed, monolith, honeycomb, etc. For example, a honeycombmonolith can comprise a single channel, the channel having a pluralityof passages, e.g., hundreds of thousands of passages per square meter ofthe honeycomb's cross-section.

The term “sorbent” means a material that removes (e.g., by sorbingand/or or attracting) a substance from another substance. For example, asorbent is a material which attracts at least one predeterminedsubstance from a mixture comprising the predetermined substance andfurther comprising at least a second substance. A sorption carried outunder “kinetic sorption conditions” is one where sorption is haltedbefore equilibrium sorption conditions are achieved. Kinetic sorptionconditions can be obtained, e.g., by operating the sorption at a higherrate per volume of sorbent, by shortening the length of the sorbent bed,etc. The term sorbent includes “absorbent” and “adsorbent.” An absorbentis a material that absorbs or incorporates a substance into the body ofthe absorbent material, which can also be referred to as absorption. Forexample, an absorbent can be used to absorb or attract or remove orextract a substance from another substance or from a mixture ofsubstances.

The term “C_(n)” hydrocarbon wherein n is a positive integer, e.g., 1,2, 3, 4, or 5, means hydrocarbon having n carbon atom(s) per molecule.The term “C_(n+)” hydrocarbon wherein n is a positive integer, e.g., 1,2, 3, 4, or 5, means hydrocarbon having at least n carbon atom(s) permolecule. The term “C_(n+)” hydrocarbon wherein n is a positive integer,e.g., 1, 2, 3, 4, or 5, means hydrocarbon having no more than n numberof carbon atom(s) per molecule. The term “hydrocarbon” means compoundscontaining hydrogen bound to carbon, and encompasses (i) saturatedhydrocarbon, (ii) unsaturated hydrocarbon, and (iii) mixtures ofhydrocarbons, including mixtures of hydrocarbons (saturated and/orunsaturated) having different values of n.

The term “alkane” means substantially saturated compounds containinghydrogen and carbon only, e.g., those containing ≤1% (molar basis) ofunsaturated carbon atoms. The term alkane encompasses C₁ to C₅ linear,iso, and cyclo alkanes.

The term “C_(n) unsaturate” means a C_(n) hydrocarbon containing atleast one carbon atom directly bound to another carbon atom by a doubleor triple bond.

The term “Periodic Table” means the Periodic Chart of the Elements, asit appears on the inside cover of The Merck Index, Twelfth Edition,Merck & Co., Inc., 1996.

The term “oxidant” means any oxygen-bearing material which, under theconditions in the reaction zone, yields an oxygen atom for oxidativecoupling and/or oxydehydrogenation. While not wishing to be limited totheory, molecular oxygen atom may be provided as a reactive gas in agaseous zone and/or atomic oxygen may be provided from a catalystsurface as, for instance in reacted or sorbed forms.

The term “oxidative coupling” refers to the oxygen-assisteddehydrogenation and coupling (formation of C—C bonds) of alkane(particularly methane) to produce water and hydrocarbon of higher order,such as producing C₂ hydrocarbon from methane. The term“oxydehydrogenation” means oxygen-assisted dehydrogenation of an alkane,particularly a C₂₊ alkane, to produce an equivalent alkene and waterwithout coupling.

The term “reaction stage” or “reactor stage” means at least oneflow-through reactor, optionally including means for conducting one ormore feeds thereto and/or one or more products away therefrom.

With respect to flow-through reactors, the term “residence time” meansthe average time duration for non-reacting (non-converting by oxidativecoupling) molecules (such as He, N₂, Ar) having a molecular weight inthe range of 4 to 40 to traverse the flow-through reactor or a definedzone within the flow-through reactor, such as a reaction zone.

With respect to flow-through reactors, the term “region” means alocation within the reactor, e.g., a specific volume within the reactorand/or a specific volume between a flow-through reactor and a secondreactor, such as a second flow-through reactor. With respect toflow-through reactors, the term “zone”, refers to a specific functionbeing carried out at a location within the flow-through reactor. Forexample, a “reaction zone” (or “reacting zone” or “reactor zone”) is alocation within the reactor for conducting a reaction, e.g., a“catalytic hydrocarbon conversion zone” is a location in the rector forcarrying out catalytic hydrocarbon conversion, such as catalyticoxidative coupling and/or catalytic oxydehydrogenation. Similarly, a“sorption zone” (or “sorbing zone” or “desorbing zone”) is a locationwithin the reactor for sorbing and/or desorbing products of thecatalytic hydrocarbon conversion, e.g., C₂₊ hydrocarbon, such as C₂₊olefin. Similarly, a “quench zone” or “quenching zone” is a locationwithin the reactor for transferring heat from products of the catalytichydrocarbon conversion, such as C₂₊ olefin.

The term “thermal catalytic oxidative coupling reactor” means anoxidative coupling reactor wherein 50.0% of the heat utilized by theoxidative coupling reaction is provided by heat transfer from at leastone thermal mass, e.g., at least one heat storage/heat transfer materialassociated with the reactor, such as tubulars or bed materials;optionally ≥80.0% or ≥90.0% of the heat utilized by the oxidativecoupling reaction is provided by such heat transfer. Optionally, a netexothermic reaction (e.g., combustion) occurs within the thermalcatalytic oxidative coupling reactor, e.g., for preheating and/orreheating the first and/or second thermal masses.

Representative Reactions

In certain aspects, the invention relates to a process for convertingreactant and oxidant in the presence of catalyst and at least onethermal mass, the catalyst and thermal mass being located in aflow-through reactor. The flow-through reactor comprises a reactorvessel configured for fluid-flow. The reactor vessel is typically in theform of an elongated vessel having at least two apertures. The firstaperture is configured for admitting fluid, e.g., a feed mixture, to thereactor. The second aperture is configured for conducting away from thereactor at least a portion of a reaction mixture produced bycatalytically reacting at least a portion of the feed mixture. Thereactor vessel can be of any cross-sectional shape, e.g., circular,elliptical, polygonal, etc. For example, the reactor vessel can be anelongated tube having a substantially circular cross section ofsubstantially constant internal diameter, the first and second aperturebeing located proximate to opposed ends of the elongated tube. Thereactor further comprises at least one hydrocarbon conversion catalyst.Typically, substantially all of the hydrocarbon conversion catalyst islocated within the reactor vessel. The hydrocarbon conversion catalystis configured for contact with the fluid-flow, e.g., with the feedmixture. The hydrocarbon conversion catalyst typically includes (i) atleast one oxidative coupling catalyst and/or (ii) at least oneoxydehydrogenation catalyst. The flow-through reactor vessel can furthercomprise at least one sorbent. Typically, the sorbent is locateddownstream of the hydrocarbon conversion catalyst with respect to thefluid-flow. Substantially all of the sorbent can be located in thereactor vessel. The sorbent can be one that is selective for olefinsorption. The sorbent is configured for contact with the fluid-flow,e.g., for contact with the reaction mixture. The flow-through reactorfurther comprises at least one thermal mass. Typically, substantiallyall of the thermal mass is located in the reactor vessel. The thermalmass is configured for thermal contact with the fluid-flow. The thermalcontact can be direct thermal contact, e.g., with the feed mixture (orone or more components thereof) and/or the reaction mixture (or one ormore components thereof). The thermal contact can be indirect thermalcontact, such as when heat is transferred between the thermal mass andthe fluid-flow through an intermediate material. Typically, the thermalmass is a solid thermal mass having passages for conducting thefluid-flow, with direct heat transfer occurring from the fluid flow toat least part of the thermal mass. Typically, a least a part of thethermal mass is located downstream of the hydrocarbon conversioncatalyst with respect to the fluid-flow. For example, at least a portionof the thermal mass can be located in the reactor vessel between thehydrocarbon conversion catalyst and the sorbent. At least a portion ofthe catalyst and/or thermal mass can be located on (or within) thethermal mass, e.g., on an internal surface of the thermal mass incontact with the fluid-flow. Typically, sorbent and hydrocarbon catalystare each located within zones of the thermal mass, e.g., a catalysiszone and a sorption (sorbing/desorbing) zone. The zones can beoverlapping or non-overlapping. Heat transfer between the fluid-flow andthermal mass is carried out in at least one heat-transfer zone. When theheat transfer includes quenching at least a portion of the reactionmixture, the heat-transfer zone is referred to as a quench zone. Whenthe heat-transfer zone is utilized for transferring heat to a feedmixture or to one or more components thereof, the heat transfer zone iscalled a pre-heat zone. When the heat-transfer zone is utilized fortransferring heat from a feed mixture or from one or more componentsthereof, the heat transfer zone is called a pre-cool zone.

The flow-through reactor is suitable for carrying out a catalytichydrocarbon conversion. In certain aspects the invention relates to analkane conversion process carried out in a catalytic flow-throughreactor. The process includes providing a first flow, the first flowcomprising alkane and oxidant and having an alkane: oxidant molar ratio≥2.0. The first flow is introduced into the reactor vessel via thevessel's upstream aperture, and flows into the reactor in an averageflow direction, from upstream to downstream. The catalytic flow-throughreactor is configured to accept the first flow. The hydrocarbonconversion catalyst has an initial average temperature in the range of550° C. to 1100° C. At least a first portion of the thermal mass islocated downstream of the hydrocarbon conversion catalyst with respectto the first flow's flow direction. The first portion of the thermalmass has an initial average temperature such that [the hydrocarbonconversion catalyst's initial average temperature−the first portion ofthe thermal mass's initial average temperature] is ≥50 C.°.

The process further includes catalytic hydrocarbon conversion, whichincludes transferring hydrogen from the alkane to the oxidant to producea reaction mixture. The catalytic transfer is carried out in thepresence of the hydrocarbon conversion catalyst. The reaction mixturecomprises (i) olefin produced by the catalytic transfer and (ii) anyunreacted alkane and/or any unreacted oxidant. The reaction mixture isquenched in the flow-through reactor by transferring heat from thereaction mixture to the thermal mass at a location downstream of thehydrocarbon conversion catalyst, downstream being with respect to thefirst flow's average flow direction. The thermal mass is cooled afterthe quenching.

The reactor can further comprise sorbent, typically located in thereactor vessel downstream of the hydrocarbon conversion catalyst.Olefin, e.g., C₂₊ olefin, such as ethylene and/or propylene, can beremoved from the quenched reaction mixture by contacting the quenchedmixture with the sorbent. Alternatively or in addition, conventionalmethods can be used for separating olefin from the quenched reactionmixture, such as one or more of those disclosed in the Backgroundreferences cited herein and in the Handbook of Petrochemicals ProductionProcesses, Robert A. Meyers, McGraw Hill, 2005, Chapters 6.1 to 6.3.After sorption, the remainder of the quenched reaction mixture (araffinate) can be conducted away from the reactor vessel via thedownstream aperture. The raffinate typically comprises at least aportion of by-products of the catalytic hydrocarbon conversion,typically one or more of water, molecular hydrogen, carbon dioxide, andcarbon monoxide. The raffinate can further comprise any unreactedcomponents of the first flow, e.g., unreacted alkane. Conventionalmethods can be used for separating unreacted alkane from the raffinate,e.g., for storage and/or further processing, such as recycle to thefirst flow.

The desired sorbate, typically C₂₊ hydrocarbon such as ethane and/orethylene, can be recovered (e.g., desorbed) from the sorbent by one ormore of (i) lessening the average total pressure proximate to thesorbent, (ii) heating the sorbent, and (iii) flowing a utility fluidproximate to the sorbent. For example, the first flow can be lessened orsubstantially halted, and a utility fluid introduced into the reactorvessel's first aperture flowing in the same average flow direction asthe first flow. Heat is transferred to the utility fluid from thehydrocarbon conversion catalyst, resulting in a cooled hydrocarbonconversion catalyst and a heated utility fluid. Heat is transferred fromthe heated utility fluid to the sorbent downstream of the hydrocarbonconversion catalyst, resulting in (a) a heated sorbent, (b) a cooledutility fluid, and (c) desorption of at least a portion of the sorbedolefin. The cooled utility fluid conveys the desorbed olefin away fromthe reactor vessel via the vessel's second aperture. Conventionalmethods can be used for separating the desired sorbate from the cooledutility fluid. Further separations can be carried out if needed. Forexample, when the desired sorbate includes ethane and ethylene, as maybe the case when the sorbent is selective for hydrocarbon sorption butless-selective for olefin sorption, further separations can be carriedout for separating ethylene from ethane.

The process can be operated continuously or semi-continuously. Forexample, in certain aspects, the flow-through reactor is substantiallyadiabatic and comprises a catalytic hydrocarbon conversion zone and aquench zone, with the catalytic hydrocarbon conversion being netexothermic. Since flow-through reactor is substantially adiabatic andthe catalytic hydrocarbon conversion reaction is net exothermic, feedmixture flow is lessened or substantially halted before that portion ofthe thermal mass in the quench zone (e.g., the first portion of thethermal mass) has an average temperature that is substantially the sameas or exceeds that of the reaction mixture entering the quench zone (atwhich point the reaction mixture would not be quenched). After feedmixture flow is curtailed or substantially halted, the catalytichydrocarbon conversion zone and quench zone can be restored to operatingtemperature, e.g., to an average temperature of the catalytichydrocarbon conversion zone in the range of 550° C. to 1100° C. and anaverage temperature in the quench zone such that [the hydrocarbonconversion catalyst's average temperature−the first portion of thethermal mass's average temperature] is ≥50° C. This can be carried outby transferring heat away from the catalytic hydrocarbon conversion zoneand the quench zone, e.g., by transferring heat away from the catalytichydrocarbon conversion catalyst and/or the thermal mass, such as fromthe first portion of the thermal mass. To do this, a flow of coolutility fluid (e.g., at ambient temperature) is introduced into thefirst aperture of the flow-through reactor. The temperature of the coolutility fluid is selected such that heat transfer to the utility fluidfrom the heated hydrocarbon conversion catalyst results in (i) anaverage temperature of the hydrocarbon conversion catalyst in the rangeof from 550° C. to 1100° C. and (ii) a moderated utility fluid having atemperature less than that of the heated quench zone. Heat is thentransferred in the quench zone from the heated first portion of thermalmass (heated as a result of the reaction mixture quenching) to themoderated utility fluid to produce a heated utility fluid and a cooledfirst portion of the thermal mass. The cooled quench zone typically hasan average temperature that is the same as or warmer than the cooledcatalytic hydrocarbon conversion zone. Additional cooling is utilized torestore the quench zone to an average temperature such that [thehydrocarbon conversion catalyst's average temperature−the first portionof the thermal mass's average temperature] is ≥50° C., e.g., byadditional heat transfer away from the thermal mass. Utility flow is nowlessened or substantially halted, and the flow of feed mixture isre-initiated to continue catalytic hydrocarbon conversion. The processis operated continuously by periodically catalytic the hydrocarbonconversion and the reactor regeneration steps, one after the other.

Representative fluids conducted into, though, and away from theflow-through reactor will now be described in more detail. The inventionis not limited to the use and/or production of these fluids, and thisdescription is not meant to foreclose the use/production of other fluidswithin the broader scope of the invention.

Feeds for the Catalytic Hydrocarbon Conversion

The hydrocarbon conversion process can be carried out by catalyticallyconverting a hydrocarbon-containing reactant (e.g., a hydrocarbonreactant, such as alkane) in the presence of oxidant, e.g., molecularoxygen. The hydrocarbon reactant and oxidant can be components of a feedmixture. The feed mixture can be produced by (i) combining hydrocarbonreactant and oxidant in the flow-through reactor, combining hydrocarbonreactant and oxidant upstream of the flow-through reactor, or acombination thereof. The feed mixture can have a hydrocarbon reactant:molecular oxygen molar ratio ≥2, e.g., ≥4, such as in the range of 2 to50, or 4 to 20.

The feed mixture is generally at least 10% (weight basis, based on theweight of the feed mixture) of the total feed to the catalytichydrocarbon conversion (the “total feed). The remainder of the totalfeed total feed can be diluent. Typically, the total feed to the reactorcomprises ≥20% feed mixture, or ≥30%, or ≥40%. Although the total feedcan consist of feed mixture, or consist essentially of feed mixture, thetotal feed can optionally comprise ≤98% feed mixture, e.g., ≤90%, suchas ≤80%, or ≤70%, with the remainder of the total feed comprisingdiluent. In certain aspects, the hydrocarbon reactant comprises ≥90%alkane (molar basis, per mole of hydrocarbon reactant), e.g., ≥99%, andthe total feed has an alkane: oxidant molar ratio in the range of 2 to50, e.g., 4 to 20. For example, (i) the hydrocarbon reactant cancomprise ≥90% methane (molar basis), e.g., ≥99%; the oxidant cancomprise ≥90% O₂ (molar basis), e.g., ≥99%; and (iii) the total feed canhave a methane:O₂ molar ratio in the range of 2 to 50, e.g., 4 to 20.

Diluent typically comprises at least one substantially inert (e.g.,unreactive) fluid, such as one or more of molecular nitrogen, water,carbon dioxide, helium, argon, etc. Optionally, the total feed comprisesdiluent in the range of from 5% (weight basis, based on the weight ofthe total feed) to 90%, or from 10% to 50%. Any convenient method orsystem can be used for adding diluent to the total feed, or one or morecomponents of the total feed. For example, at least a portion of thetotal feed's diluent can be added to one or more of (i) the hydrocarbonreactant (e.g., to the alkane component), (ii) the oxidant, (iii) thefeed mixture, and (iv) the total feed. Conventional equipment can beutilized for adding diluent to the total feed or one or more componentsthereof, e.g., by way of one or more steam spargers when the diluentincludes steam, but the invention is not limited thereto.

The hydrocarbon reactant can comprise alkane, e.g., one or more of C⁵⁻linear, C⁵⁻ iso, and C⁵⁻ cyclo alkane. Generally, the hydrocarbonreactant comprises one or more of methane, ethane, propane, butane andpentane. Particular examples include methane, ethane and propane, withmethane being a preferred alkane. The hydrocarbon reactant typicallycomprises ≥10% (molar basis, per mole of hydrocarbon reactant) alkane,e.g., ≥25%, such as ≥50%, or ≥75%, or ≥90%, or ≥99%. For example, thehydrocarbon reactant can consist of alkane, or consist essentially ofalkane. In certain aspects, the alkane comprises ≥75% methane, or ≥90%,or ≥99%. In other aspects, the alkane comprises ethane and/or propane,e.g., ≥75% ethane and/or propane, or ≥90%, or ≥99%. In other aspects,the alkane comprises a mixture of methane, ethane, and propane, e.g., amixture comprising ≥25% methane, ≥5% ethane, and ≥1% propane, such as25% to 94% methane, 5% to 50% ethane, and 1% to 50% propane. In certainaspects, (i) the alkane comprises methane and (ii) the feed mixture hasa methane:oxidant molar ratio in the range of from 2 to 50, or about 4to 20.

The oxidant typically comprises one or more fluids which yield oxygenunder the specified hydrocarbon conversion conditions. Typically, theoxidant includes one or more of molecular oxygen (O₂), O₂ ⁻, O₂ ⁻,ionized oxygen atoms, nitrogen oxides such as N₂O, etc. Oxidant istypically in the vapor phase at the specified hydrocarbon conversionconditions, but this is not required, and in certain aspects liquidand/or solid oxidant can be used. The oxidant can comprise O₂, e.g.,≥90% O₂ (molar basis, per mole of oxidant), such as, ≥99%. For example,the oxidant can comprise O₂ in air, or O₂ obtained or derived from air,e.g., by separation. The oxidant can comprise (or consist essentiallyof, or consist of) air. When the oxidant comprises O₂ in air, the totalfeed generally comprises at least a portion of the air's molecularnitrogen as diluent. In other words, when the oxidant comprisesmolecular oxygen in air, other gasses in the air, such as molecularnitrogen, are considered to be diluent, and are not considered to bepart of the oxidant.

The total feed can optionally comprise (i) ≥10% alkane (weight basisbased on the weight of the total feed), e.g., ≥25%, or ≥50%, or ≥75%, or≥90%, or ≥95%, or ≥98% of the total feed; and/or (ii) ≤90%, or ≤80%, or≤70% of the total feed. The oxidizing component of the first mixture,e.g., oxidant, can comprise at least 2 wt. % of the total feed providedto the reactor, based on total weight of the feed provided to thereactor. The total feed can optionally comprise (i) ≥5% oxidant (weightbasis, based on the weight of the total feed), or ≥10%, or ≥20% of thetotal feed or (ii) ≤90%, or ≤80%, or ≤60%, or ≤40%. In certain aspects,total feed comprises ≥10% alkane and ≥2% oxidant (both percents based onthe total feed's weight).

Hydrocarbon Conversion Catalyst

The catalytic hydrocarbon conversion utilizes at least one hydrocarbonconversion catalyst. Any hydrocarbon conversion catalyst capable ofcarrying out the specified catalytic conversion of the specifiedhydrocarbon reactant and specified oxidant can be used. Particularlyuseful hydrocarbon conversion catalysts include oxydehydrogenationcatalysts and oxidative coupling catalysts, such as metal oxidehydrocarbon conversion catalysts useful in oxydehydrogenation andoxidative coupling reactions. The metal oxide catalysts also includemixed metal oxide catalysts, meaning that there may be more than onemetal element in the oxide catalyst. Particularly useful metal oxidecatalysts are metal oxide catalysts effective in catalyticallyconverting alkane (e.g., methane) to C₂₊ olefin (e.g., ethylene).

Suitable metal oxide catalysts include those which comprise at least onebase metal of IUPAC Group 2, Group 3, Group 7, Group 8, Group 9, Group14, Group 15 and the lanthanide series of metals of the Periodic Table.Examples of Group 1 metals include Li, Na, K, Rb, Cs and Fr. Li, Na, K,Rb and Cs represent more common Group 1 metals. Examples of Group 2metals include Be, Mg, Ca, Sr, Ba and Ra. Mg, Ca, Sr and Ba are morecommon Group 2 metals. Examples of Group 3 metals include Sc, Y, La andAc. La is an example of a particularly common Group 3 metal. Examples ofGroup 7 metals include Mn and Re. Mn is an example of a particularlycommon Group 7 metal. Examples of Group 8 metals include Fe, Ru and Os.Fe is an example of particularly common Group 8 metal. Examples of Group9 metals include Co, Rh and Ir. Co is an example of particularly commonGroup 9 metal. Examples of Group 14 metals include Sn and Pb. Pb is anexample of a particularly common Group 14 metal. An example of a Group15 metal includes Bi. Examples of the lanthanide series of metalsinclude Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu. Sm, Gd,Ho, and Yb are more common lanthanide metals.

Suitable hydrocarbon conversion catalysts, including those that can beused for oxidative coupling, are disclosed in U.S. Pat. No. 6,096,934,which is incorporated by reference herein in its entirety. Suchcatalysts include lithium supported on magnesium oxide where the lithiumis present in either the hydroxide or oxide form; bismuth supported oncalcium oxide where the bismuth is present in either the hydroxide oroxide form; lithium supported on calcium oxide where the lithium ispresent in either the hydroxide or oxide form; cerium supported onmagnesium oxide where the cerium is present in either the hydroxide oroxide form; nickel and lanthanum supported on magnesium oxide where thelanthanum is present in either the hydroxide or oxide form and thenickel is present in the metallic form; and lithium supported onlanthanum oxide where the lithium is present in either the hydroxide oroxide form; or any other metal or metal oxide or hydroxide catalystpromoted with a Group 1, 2, or lanthanide series element present in anoxide or hydroxide form.

Other suitable hydrocarbon conversion catalysts are disclosed in U.S.Pat. No. 5,245,124, and in Y. A. Amenomiya et al. in “Conversion ofMethane by Oxidative Coupling,” report to CANMET, Energy, Mines andResources, Ottawa, Canada, both being incorporated by reference hereinin their entirety. In order of preference, suitable hydrocarbonconversion catalysts of these references includeLi/Sm₂O₃>Na/CaO>K/CaO>LaAl₂O₃>Sm₂O₃>Li/CaO>PbO>Bi₂O₃>Ho₂O₃>Gd₂O₃>Li/MgO>Li/CaO˜Yb₂O₃>Y₂O₃Na/MgO˜CaO>MgO.Additives to the catalysts include Ba, Li, Sr, Pb, K, Mg, Ca, Na, andSb.

Perovskites are also useful for the specified catalytic hydrocarbonconversion of the specified hydrocarbon reactant and specified oxidant.Suitable perovskites include those having the formula A₂B₂C₃O₁₀, where Ais alkali metal; B is lanthanum or a lanthanide element, for example,cerium, neodymium, samarium, praseodymium, gadolinium or dysprosium; andC is titanium. A particular example is disclosed in U.S. Pat. No.5,026,945, which is incorporated by reference herein in its entirety.The disclosed perovskites include those having the formulaA_(x)Ln_(y)Ti_(z)O₁₀, wherein A is one or more alkali metal; Ln is oneor more of lanthanum, cerium, neodymium, samarium, praseodymium,gadolinium and dysprosium; x is about 2; y is about 2; and z is about 3.

One or more of the hydrocarbon conversion catalysts can be incorporatedin the specified flow-through reactor, e.g., in a configuration in whichthe hydrocarbon reactant and oxidant to catalytically react with oneanother as the hydrocarbon reactant and oxidant transit the flow-throughreactor. For example, the hydrocarbon conversion catalyst (and/or one ormore components thereof) can be arranged in at least one catalyst bed.The catalyst bed can be located within the flow-through reactor andconfigured so that one or more of the bed surfaces is exposed tohydrocarbon reactant and/or oxidant transiting the flow-through reactor.Alternatively, or in addition, the hydrocarbon conversion catalyst canbe located proximate to one or more thermal mass, e.g., by incorporatingat least a portion of the hydrocarbon conversion catalyst in and/or on athermal mass, e.g., as a coating. For example, the hydrocarbonconversion catalyst (and/or components thereof) can be arranged at oneor more surfaces of at least one thermal mass over which the feedcomponents pass, e.g., proximate to that portion of the thermal mass'ssurface area exposed to hydrocarbon reactant and/or oxidant, such as thethermal mass's interior surface area, including the surface area of thethermal mass's internal passages or channels.

Catalytic Hydrocarbon Conversion

Main conversion reactions in the reaction zone section of the reactor,when the feed to the reactor is comprised of methane and oxygen, are theexothermic reactions to C₂ products:CH₄+¼O₂→½C₂H₆+½H₂O ΔH=−87 kJ/mol  (1)CH₄+½O₂→½C₂H₄+H₂O ΔH=−192 kJ/mol  (2)

and optionally combustion, which consumes more oxygen and generates moreheat:CH₄+1½O₂→CO+2H₂O ΔH=−519 kJ/mol  (3)CH₄+2O₂→CO+2H₂O ΔH=−802 kJ/mol  (4)It has been found that by regulating the relative amount of reactant andoxidant to the relative amounts specified for the feed mixture, reaction(1) and preferably reaction (2) can be favored over reactions (3) and(4), and over reactions which combust one or more of the desiredproducts. Such undesirable combustion reactions includeC₂H_(x)+O₂→CO₂+H₂O, such as C₂H₄+3O₂→2CO₂+2H₂O (−1412 kJ/mol) andC₂H₆+7/2O₂→2CO₂ 3H₂O (−1517 kJ/mol).

Accordingly, the catalytic hydrocarbon conversion process, e.g., theoxidative coupling of C₁ hydrocarbon and/or the oxydehydrogenation ofC₂₊ hydrocarbon, can be carried out in one or more of the specifiedflow-through reactors in the presence of one or more of the specifiedhydrocarbon conversion catalysts at the specified temperatures andpressures. For example, the catalytic hydrocarbon conversion process isparticularly efficient when carried out at reaction zone temperatures offrom 550° C. to 1100° C. Alternatively, the hydrocarbon conversionprocess is particularly efficient at reaction zone temperatures of from650° C. to 900° C., or at temperatures of from 675° C. to 825° C.

Operating pressures may include a pressure of at least atmosphericpressure (zero pressure, gauge), such as ≥4 pounds per square inch gauge(psig) (28 kilo Pascals gauge (kPag)), or ≥15 psig (103 kPag), or ≥36psig (248 kPag), or ≥44 psig (303 kPag), or ≥103 psig (700 kPag), butmay be 300 psig (2064 kPag), or ≤163 psig (1121 kPag), or ≤150 psig(1032 kPag).

Residence time in the flow-through reactor, e.g., in the catalytichydrocarbon reaction zone of the flow-through reactor is typically ≤20seconds, e.g., ≤10 seconds, such as ≤5 seconds, or in the range of 0.01seconds to 20 seconds, or in the range of from 0.5 seconds to 10seconds. Also, as may be appreciated, these different pressures andtemperatures may be utilized together to form different combinationsdepending on the specific configuration of equipment.

Thermal Mass

The flow-through reactor includes at least one thermal mass. Forexample, at least a portion of the thermal mass configured so that theit is in thermal contact (direct or indirect) with the reaction mixtureproduced by the specified catalytic hydrocarbon conversion, andoptionally in thermal contact (direct or indirect) with at least onecomponent of the total feed, e.g., at least one of the hydrocarbonreactant, the oxidant, and the diluent. The thermal mass is selectedfrom among materials which are capable of transferring heat to and/orfrom (i) the specified feed mixture or one or more components thereofand (ii) storing heat. At least a portion of the thermal mass is locatedwithin the flow-through reactor in a quench zone of the flow-throughreactor that is located downstream (with respect to average flow of thespecified reaction mixture) of the flow through reactor's catalytichydrocarbon conversion zone.

Generally, at least a portion of the thermal mass is located within theflow-through reactor for quenching the specified reaction mixture,typically in at least one quench zone. Besides the quench zone, athermal mass or portion thereof can be located in the flow-throughreactor proximate to one or more of the catalytic hydrocarbon conversionzone, the quench zone, and the sorption zone. When the thermal massencompasses more than one zone (more than one of a catalytic zone, aquench zone, and a sorbent zone), there need not be any physicalmanifestation within the thermal mass of the zone's beginning or end. Itmay simply be a mathematical construct defining an area or volume withinan otherwise homogenous thermal mass.

The thermal mass can be of substantially any form or shape, such as, butnot limited at least one of spheres, beads, honeycomb materials, a tube,pipe, U-tube, fluid mixer, nozzle, extruded monolith, brick, tile,catalyst tray, reactor tray, tray component, valves, and/or otherrefractory components that are exposed to high temperature. The thermalmass can be segmented, with each segment having a first end (e.g., abeginning) and a second end (e.g., an ending). Each end is representedby a cross sectional area that is approximately orthogonal to average(or net) flow direction, e.g., the first end corresponds to the upstreamend and the second end corresponds to the downstream end of the thermalmass or thermal mass segment. The thermal mass or portion thereof can bein monolith form. When a thermal mass includes a plurality of monoliths,the individual monoliths can be arranged in parallel, series and/orseries parallel. Suitable monoliths include those formed by extruding ordie pressing ceramic into particular shapes, e.g., polygonal shapes,such as shapes having regular polygonal cross-section, such astriangular, rectangular, hexagonal, star, etc. cross-section. Shapedmonoliths can be stacked, e.g., into two- or three-dimensionally stacks,such as blocks above, behind, and beside each other. Monoliths areparticularly effective as thermal mass because they provide high heattransfer capacity with lessened pressure drop. The shape of the thermalmass is not restricted to any particular geometry. For example, thethermal mass can be elongated, and can have elliptical, cylindrical,and/or rectangular cross-sections, including combinations thereof. Aplurality of thermal masses can be of the same shape and size, but thisis not required. A thermal mass can be in the form of one or morehoneycomb monoliths of substantially cylindrical cross-section. Thermalmass channels can comprise a plurality of passages (e.g., those in aconceptual or physical “pie-slice” of the monolith's cross-sectionalarea. The passages of each channel typically comprise substantiallyparallel, substantially independent flow-paths within the honeycomb. Thepassages within the reacting, quenching, and or sorbing zones of athermal mass can each be of the same size and shape.

In certain aspects, one or more of the thermal masses includes separatepassages through reactor components to manage the flow of one or morecomponents of the reaction mixture and/or the feed mixture through thethermal mass. The passages and/or channels can be separate, e.g.,passages that comprise flow barriers that effectively function as wallsto lessen or prevent cross flow or mixing of fluids (e.g., reactantsand/or products) between passages, except in the desired regions of thereactor. Suitable thermal masses include those having a plurality ofpassages, which are typically configured for parallel-flow, e.g.,channeled thermal masses comprising one or more honeycomb monoliths.Typical honeycomb monoliths include a plurality of parallel channels,each channel comprising a plurality of passages, the passages beingarranged in parallel fashion with walls serving to separate eachpassage.

Typically, one or more thermal mass is configured proximate to at leastone catalyst bed used for carrying out the specified catalytichydrocarbon conversion. For example, the thermal mass can comprise oneor more multi-functional, refractory honeycomb, e.g., one having atleast (i) sorbent functionality, (ii) heat transfer/heat storagefunctionality, and (iii) catalytic functionality for one or more of thespecified catalytic hydrocarbon conversion reactions. Optionally, atleast a portion of the sorbent functionality is located in or proximateto one or more of the passages through the honeycomb, in fluidic-contactwith the specified reaction mixture. Optionally, at least a portion ofthe catalytic functionality is located in or proximate to one or more ofthe passages through the honeycomb, in fluidic-contact with one or moreof the specified feed mixture (or one or more components thereof),and/or the specified reaction mixture (or one or more componentsthereof). The catalytic functionality of the refractory monolith istypically located downstream of the flow-through reactor's inletaperture, with downstream being with respect to the average flow of feedmixture, At least a portion of the thermal mass functionality istypically located downstream of the catalytic functionality. The sorbentfunctionality can be co-located with the thermal mass functionality, butthis is not required, and in certain aspects at least a portion of thesorbent functionality is located downstream of the thermal massfunctionality.

When a segmented thermal mass is used, one or more mixer/distributormeans can be used between thermal mass segments, e.g., to improve theoxidative coupling reaction. Mixer mechanisms, distributor mechanisms,reactor system internals, flow-control mechanisms, etc., for the reactorcan be substantially the same as those described in U.S. Pat. No.7,943,808 and/or U.S. Patent Application Publication No. 2013/157205,for example.

The thermal mass can include material typically used in fabrication ofat least one of a honeycomb monolith, a reactor bed, a reactor conduit,a reactant mixer, a reactant distributor, and a reactantmixer/distributor. Thermal mass can be selected from any material whichcan maintain integrity, functionality, and withstand long term exposureto the relevant temperatures for the oxidative coupling and combustionreactions. Non-limiting examples of such materials include one or moreof glass or ceramic beads or spheres, metal beads or spheres, ceramics,ceramic or metal honeycomb materials, ceramic tubes, extruded monoliths,and the like. In particular aspects, the thermal mass is capable ofabsorbing and storing heat and releasing the stored heat, without anysignificant phase change, over a temperature range in which thespecified catalytic hydrocarbon conversion (and optional hydrocarboncombustion) are carried out. Examples of temperature ranges at which thethermal mass absorbs, stores and releases heat include a range of from50° C. to 1500° C., alternatively from 100° C. to 1500° C. or from 200°C. to 1500° C.

The thermal mass and the materials from which thermal mass is madeand/or includes can be characterized by one or more properties.

Melting temperatures (melting points) are reflective of the ability ofthe thermal mass to withstand combustion and oxidative couplingtemperatures without chemical change and/or physical destruction.Thermal masses having higher melting points are preferred according tothis invention. For example, the melting point (or decompositiontemperature) of the thermal mass of this invention is preferably atleast 1200° C., or at least 1500° C., measured at atmospheric pressure.

Porosity is a measure of the effective open pore space in the thermalmass into which heat and gasses can penetrate and eventually degrade thestructure. The porosity of a thermal mass can be expressed as theaverage percentage of open pore space in the overall refractory volume.As an example, the thermal masses utilized in certain aspects of theinvention can have a porosity of not greater than 50%, or not greaterthan 40%, or not greater than 30%. The porosity can be measured by anArchimedes process, e.g., mercury porosimitry.

Bulk density is a measure of the weight of a given volume of the thermalmass. Higher bulk densities, with lower porosities, can be particularlyeffective. As an example, the thermal masses can have a bulk density ofat least 0.5 g/cm³. For example, the bulk density can be from 0.5 g/cm³to 3.5 g/cm³ or from 1 g/cm³ to 3 g/cm³.

Thermal conductivity is defined as the quantity of heat that will flowthrough a unit area in direction normal to the surface area in a definedtime with a known temperature gradient under steady state conditions.Thermal conductivity represents a general heat flow characteristic ofthe thermal mass. Higher thermal conductivity thermal masses arepreferred. For example, the thermal mass can have a thermal conductivityof from 0.1 W/mK to 50 W/mK or from 0.2 W/mK to 30 W/mK.

Thermal expansion of the thermal mass should not be so great such thatcracking of the material occurs during operation of the reaction system.In one aspect, the thermal mass can be characterized by a thermalexpansion coefficient. For example, the thermal mass can have a thermalexpansion coefficient of from 0.1×10⁻⁶/K to 20×10⁻⁶/K or from 0.2×10⁻⁶/Kto 15×10⁻⁶/K. In this example, the thermal expansion coefficient isgiven as a value in a temperature range of from 25° C. to 800° C.

Thermal capacity is the ability of a material to hold heat. The thermalmasses can have a higher thermal capacity, but not so high as toincrease the probability of cracking at higher temperatures. Forexample, the thermal masses utilized in certain can have a thermalcapacity of from 250 Jm³/K to 4500 Jm³/K or from 500 Jm³/K to 3000Jm³/K.

For thermal mass located in or proximate to a sorbent zone, the thermalmass itself can have sorbing functionality. For example, certainceramics can act as a sorbent, while also functioning to adsorb and/orrelease heat. Thus, the thermal mass can be one material that isbi-functional.

The thermal mass or portion thereof can be in the form of bedding and/orpacking material, e.g., one or more of beads or spheres; monoliths(e.g., extruded honeycomb and/or tubes), catalysts; checker bricks, andtiles. Suitable thermal masses include those comprising ceramic, e.g.,one or more yttria, zirconia, alumina, silica, and other refractorymaterial capable of adsorbing, storing and transferring heat, and thatare effective in withstanding temperatures within the oxidative couplingreactor. The ceramic can be vitreous or non-vitreous, but is typicallynon-vitreous.

At each step of the process, a specified zone has a characteristic“average zone temperature” that is an average over all locations in thezone, from the beginning of the zone to the end of the zone, and over aspecified period of time. For example, the average zone temperature of areaction zone during catalytic hydrocarbon conversion can be determinedas an average temperature from the beginning of the reaction zone to theend, which is determined over the time period reactants arecatalytically reacting the zone. To compare average zone temperatures,such as the average zone temperature of a reaction zone to (i) asorption zone during sorption or (ii) a heat transfer zone during heattransfer, the average temperature from the beginning of a zone to theend of a zone are preferably determined over comparable time periods inwhich fluids flow through the respective zones. Although the thermalmass can be in thermal equilibrium at a substantially constanttemperature over all its locations, this is not required, and in certainaspects a thermal mass exhibits temperature profile indicating aprogression or decrease in temperature across the thermal mass. This canbe the case when there is heat exchange between fluid flowing throughthe thermal mass and the thermal mass itself.

Thermal mass characteristics and configurations can be characterized interms of tortuosity (τ), void fraction (ε) and wetted area (a_(v)).Within any zone, the thermal mass can have a constant or non-constanta_(v). If the zone is homogenous in contents, a_(v) will be constantthroughout the zone. If the zone is inhomogeneous, then a_(v) should betaken as a volume average over the zone.

Tortuosity tends to impact the momentum transfer rate more than the heattransfer rate, so low tortuosity packing is typically utilized (e.g.,straight-channel honeycombs, such as one or more channels having aplurality of parallel passages). Void fraction determines the ratio ofheat-storing solids in the bed relative to the fluid-carrying passages,and it can be adjusted over a wide range without impacting the heattransfer rate or momentum transfer rate. Wetted area directly relates tocertain heat transfer properties, such as convective heat transfer andconductive heat transfer, while also directly relates to the momentumtransfer rate. The impact of wetted area is similar for convective heattransfer and momentum transfer rate. Thus, for flow-through reactorsemploying convective heat transfer, the selection of wetted areaprovides a design tradeoff between high heat transfer (efficiency andselectivity) versus high momentum transfer, which manifests as pressuredrop, e.g., resulting in reactor design difficulties.

A specific wetted area can be used in a specific zone of theflow-through reactor, e.g., in a specific zone of the thermal mass. Thespecific wetted area is selected based on the dominant heat transfermode at the specified zone, e.g., via radiation, convection, conduction,or some combination thereof. For example, a first portion of a thermalmass, e.g., a portion located in a catalytic hydrocarbon conversionzone, can include passages having a wetted area a_(v1), while a secondportion of the thermal mass, e.g., a portion located in a quenchingzone, can include passages having a second wetted area a_(v2). Thewetted areas a_(v1) and a_(v2) can be different (e.g., a_(v1)≠a_(v2))and may include wetter areas a_(v1) and a_(v2) being different from eachother by at least 25%, at least 30%, at least 40% or at least 50%.

The thermal mass may include (i) a first channel (e.g., for hydrocarbonreactant) comprising a first plurality passages and having a firstwetted area a_(v1); and (ii) a second channel (e.g., for oxidant)comprising a second plurality of passages and having a second wettedarea a_(v2), wherein (i) a_(v1)≠a_(v2) and (ii) a_(v2) is different froma_(v1) by at least 25%. The difference percentage for a_(v), as usedherein, is defined to be based on the higher of the two wetted areas.For example, if a_(v1)≥a_(v2), then the percent difference betweena_(v1) and a_(v2) is 100*(a_(v1)−a_(v2))/a_(v1).

Sorbents

The flow-through reactor optionally comprises sorbent, e.g., sorbentlocated in a sorbent zone within the flow-through reactor. Sorbent, whenused, can be configured to selectively remove or extract hydrocarbonfrom other components of the reaction mixture produced by the specifiedcatalytic hydrocarbon conversion. For example, the sorbent can beselected from among those that are selecting for removing from thereaction mixture one or more of C₂₊ hydrocarbon, e.g., C₂₊ unsaturates,such as C₂₊ olefin, particularly ethylene and/or propylene. The sorbentcan be located within the flow-through reactor, e.g., at a locationdownstream of the thermal mass, but this is not required. In certainaspects, the sorbent is located within the flow-through reactorproximate to at least a portion of the thermal mass, e.g., in or on atleast a portion of the thermal mass, such as in or on that portion ofthe thermal mass that is located in the flow-through reactor's quenchzone. In other words, the sorption zone and quench zones of can beoverlapping zones of the flow-through reactor.

When used, sorbent can be located in a sorption zone of the flow-throughreactor that is downstream of the catalytic hydrocarbon conversion zone.A quench zone, comprising thermal mass can be located between thecatalytic hydrocarbon conversion zone and the quench zone. Duringsorption, the average zone temperature in the sorption zone is typicallyat an average zone temperature that is lower than that of the averagezone temperature within the catalytic hydrocarbon conversion zone. As anexample, the sorption zone (during sorption) can be at an average zonetemperature of at least 50° C., or at least 100° C., or at least 200° C.lower than the average zone temperature within the catalytic hydrocarbonconversion zone. Although sorption can be carried out in equilibrium,the flow-through reactor is typically operated under kinetic sorptionconditions, particularly when the flow-through reactor is a reverse-flowreactor.

In a case in which the sorbate includes at least one of ethylene andpropylene, sorption can be carried out at a temperature ≥150° C., e.g.,≥200° C., or ≥250° C., such as in a range of from 150° C. to 500° C., or200° C. to 475° C. Alternatively, in a case in which the sorbateincludes at least one of ethylene and propylene, sorption can be carriedout at a temperature range of from 100° C. to 400° C., or from 150° C.to 350° C., or from 200° C. to 300° C.

Pressure at which sorption is carried out is typically within thepressure range of the reaction zone. As a practical matter, the pressurecan be less than that of the reaction zone, since the sorption zone isgenerally downstream of the reaction zone and some pressure drop willnaturally occur due to typical physical constrains within the reactor.

Suitable sorbents include high surface area, porous materials which havebeen treated with metal species capable of π-complexation with olefins,such as copper and silver salts. Such sorbents are described in U.S.Pat. No. 4,917,711, which describes the use of supports such as zeolite4A, zeolite X, zeolite Y, alumina and silica, each treated with a coppersalt, to selectively remove carbon monoxide and/or olefins from agaseous mixture containing saturated hydrocarbons (i.e. paraffins) suchas ethane and propane.

Suitable sorbents include those which comprise copper salts and silvercompounds supported on one or more of silica, alumina, MCM-41 zeolite,4A zeolite, carbon molecular sieves, polymers such as Amerberlyst-35resin, and alumina.

Suitable clay-based sorbents, including Ag⁺+ impregnated clay sorbents,are disclosed in U.S. Pat. Nos. 6,867,166 and 6,423,881, which areincorporated by reference herein in their entirety, and in Choudary etal., Ind. Eng. Chem. Res. 2002, v 41, p. 2728, which is alsoincorporated by reference herein in its entirety. Other useful sorbentsare described in U.S. Pat. Nos. 4,717,398; 6,200,366; and 5,365,011, andin Van Miltenburg et al., Chemical Engineering Research and Design,2006, 84(A5) p. 350, all of which are incorporated by reference hereinin their entirety. These references disclose modified Faujasitezeolites, which are used for the separation of ethylene fromethylene/ethane mixtures. Suitable sorbents can be selected from amongaluminophosphates, such as described in U.S. Pat. No. 6,293,999, whichis incorporated by reference herein in its entirety. Analogous zeolitesorbents can also be used. Particularly suitable sorbents include one ormore metal-organic frameworks which are capable of selectivelyseparating olefin (e.g., C³⁻ olefin) from fluid mixtures (such as C⁴⁻hydrocarbon mixtures), e.g., one or more of which having at least oneFe-organic framework. Suitable metal-organic frameworks having aredox-active metal center (e.g., Fe2(dobdc)), are disclosed in U.S.Patent Publication No. 2013/0053585, which is incorporated by referenceherein in its entirety.

Following sorption of the desired sorbate, raffinate is conducted awayfrom the sorbtion zone. The raffinate is lean of the sorbate, andtypically comprises an amount of the desired sorbate that is ≤0.5 timesthe amount of the desired sorbate in the reaction mixture. Theappearance of an increased amount of the desired sorbate in theraffinate (called “break-through”) is an indication that the sorbent isapproaching its ultimate capacity. Within a predetermined time before,at, or after break-through, the passing of the reaction mixture to thesorbent can be lessened or discontinued, in order to desorb sorbate fromthe sorbent.

When the sorbent is one that is selective for sorbing C₂ hydrocarbonfrom the reaction mixture, desorption is carried out in order to (i)regenerate the one C₂-selective sorbent (to restore capacity for sorbingthe reaction mixture's C₂ composition) and (ii) to recover the desorbedC₂ composition. Conventional sorbent regeneration conditions aresuitable. Desorption be carried out by a reduction in temperature,pressure or both.

The sorption zone typically has an average zone temperature duringdesorption that is at least 4° C. higher than the average sorption zonetemperature during sorption. For example, desorption can be carried outat an average sorption zone temperature of at least 5° C., or at least6° C. above that for sorption of the sorbate. Desorption of the sorbatecan be carried out at a temperature that is 4° C. to 200° C. greaterthan that for sorption of the sorbate.

Optionally, a sweep fluid is used for the desorption and/or to assistdesorbing the C₂ composition. Typical sweep fluids include relativelyinert liquids and vapors, especially those which are relatively easy toseparate from the desorbed C₂ composition. Steam and/or molecularnitrogen are suitable sweep fluids. C₂ unsaturates can be separated fromthe C₂ composition, e.g., for storage and/or further processing, such asthe polymerization of ethylene obtained from the C₂ composition.Desorption is typically continued until the amount of the desiredsorbate in the desorption effluent is less than a pre-determined amount,after which the desorption can be halted. Although desorption can becarried out in equilibrium, desorption is typically carried out underkinetic desorption conditions, particularly when the flow-throughreactor is a reverse-flow reactor.

In certain aspects, desorption of the sorbate, i.e., desorption of theolefin sorbed from the reaction mixture, is carried out in theflow-through reactor's sorption zone at an average temperature that isless than that of the average temperature in the flow-through reactor'scatalytic hydrocarbon conversion zone reaction during the catalytichydrocarbon conversion, e.g., at least 400° C. less. Average zonetemperature of any zone is calculated as the arithmetic mean temperatureof the zone. At least two pints are utilized in determining average zonetemperature, typically a first point proximate to a first end of thezone and a second point proximate to the opposite end. It is preferableto utilize at least a third point, e.g., one located proximate to thecenter of the zone.

Reverse-Flow Reactors

Catalytic regenerative, reverse-flow reactors can be used to carry outthe hydrocarbon conversion. A regenerative, reverse-flow reactor is (i)“reverse flow” in the sense that an upstream region of the reactor withrespect to the average flow of a first feed mixture corresponds to thedownstream region with respect to the average flow of a second feedmixture and (ii) “regenerative” in the sense that at least a portion ofany heat lost (e.g., by radiation) during the specified catalyticconversion of the specified first feed mixture is provided by thespecified catalytic hydrocarbon conversion of the specified second feedmixture. Reverse-flow reactor cycles typically are either symmetric orasymmetric. Asymmetric cycles are typically used to execute endothermicchemistry, and the desired endothermic chemistry is paired with adifferent chemistry that is exothermic (typically combustion) to provideheat of reaction for the endothermic reaction.

A variety of reverse-flow reactors can be utilized, e.g., alone or incombination with other flow through reactors, including otherreverse-flow reactors. For example, a reverse-flow reactor may include ahousing, a plurality of input means (e.g., conduits and valves), one ormore insulation components (e.g., insulation bricks) and one or moreprocess flow components (e.g., thermal mass, mixing components, etc.).The housing may be utilized to enclose an interior region and has one ormore insulation components disposed adjacent to the housing. Theplurality of input means may include one or more conduits and one ormore valves that are configured to manage the flow of one or morestreams into the interior region from a location external to theinterior region or housing, e.g., via first and second apertures.Process flow components can be configured and/or arranged to manage theflow of fluids through the interior region, wherein the one or moreprocess flow components may include a thermal mass having differentportions with each having different flow-paths and wetted area. Inaspects where the first and/or second mixtures are combined in areverse-flow reactor, one or more mixer or mixer-distributors can beused for the mixing. Regenerative reverse-flow reactors may involvemultiple steps repeated in sequence to form a cycle for the process.That is, the specified catalytic hydrocarbon conversion can include twoor more sequential steps, which include an optional regeneration step toheat or preheat the zones containing the thermal mass and an oxidativecoupling reaction step that converts the hydrocarbons in a first feedmixture into a first reaction mixture during catalytic hydrocarbonconversion mode. When the specified catalytic hydrocarbon conversion isnet exothermic or insufficiently exothermic to make-up heat lossesresulting from, e.g., one or more of convection, additional regenerationcan be provided during an additional regeneration mode. The additionalregeneration can be carried out by conducting a heated utility fluidthough the reverse-flow reactor. Alternatively or in addition, a flow ofat least one combustion mixture of fuel, oxidant, and/or a supplementalamount of one of these reactants, can be provided directly to a locationalong the flow path within the reactor (e.g., a mixing zone). Thedelivered reactants in the combustion mixture then exothermically react(combust) and heat the thermal mass. According to one aspect, thecombustion reaction can be carried out to heat the thermal massesbefore, during and/or after one or more intervals of the oxidativecoupling reaction. For example, a combustion reaction can be carried outto initially heat (e.g., preheat) one or more thermal masses of thereverse-flow reactor. Combustion products can then be exhausted and afirst feed mixture, such as a combination of alkane and oxidant, can beintroduced into the reactor and exposed to the heated catalyst in orderto catalytically transfer hydrogen in a reacting zone from the firstfeed mixture's alkane to the first feed mixture's oxidant.

In certain aspects, the flow-through reactor comprises at least onereverse-flow reactor. The reverse-flow reactors can be similar in formto those conventional reverse-flow reactors used for crackingsubstantially saturated hydrocarbons to produce acetylene, e.g., thosedescribed in U.S. Pat. Nos. 7,943,808, 7,491,250, 7,846,401, and7,815,873. The reverse-flow reactors of the invention differ fromconventional reverse-flow reactors in that the reverse-flow reactors ofthe invention contain at least one of the specified catalytichydrocarbon conversion catalysts in the specified location with respectto at least one thermal mass.

The reverse flow reactor can be operated similarly to thepreviously-described flow-through reactors, except that in at least onestep of the process (e.g., the thermal mass regeneration step and/or thesorbent desorption step) is carried out in reverse-flow. In other words,the specified feed mixture can be admitted to the first aperture of therevere-flow reactor, with the specified feed mixture then transiting thereverse-flow reactor downstream toward the quench zone. The quenchedreaction mixture is conducted away from the second aperture of thereverse-flow reactor, e.g., for removal of the desired C³⁻ olefin. Flowof the feed mixture is then lessened or substantially halted. In aspectswhere the catalytic hydrocarbon reaction is net-exothermic, a flow ofutility fluid flow can then be established in the reverse-flow direction(reverse with respect to the average flow of feed mixture and reactionmixture) in order to remove heat from one or more regions of thereverse-flow reactor. For example, a cool utility fluid (e.g., one atambient temperature) can be introduced into the second aperture of thereverse-flow reactor, with the utility fluid flowing downstream (withrespect to average flow of the utility fluid) toward the flow-throughreactor's quench zone. Heat is transferred to the utility fluid in thequench zone, e.g., heat the cooled utility fluid to restore the quenchzone to substantially its initial average temperature at the start offorward-flow. The heated utility fluid continues to transit thereverse-flow reactor downstream toward the catalytic hydrocarbonconversion zone. Heat is transferred to the heated utility fluid in thecatalytic hydrocarbon conversion zone, e.g., to further heat the heatedutility fluid and to restore that zone substantially to an averagetemperature suitable for carrying out the catalytic hydrocarbonconversion in a subsequent forward flow. Since cooled utility fluid isintroduced into the second aperture of the reverse-flow reactor, withthe further-heated utility fluid removed from the first aperture, heattransfer to the utility fluid will (i) restore the hydrocarbonconversion catalyst of the catalytic hydrocarbon conversion zone to anaverage temperature in the range of 550° C. to 1100° C. and (ii) restorethat portion of the thermal mass (the first portion) located in thequench zone to an average temperature such that [the hydrocarbonconversion catalyst's average temperature −the first portion of thethermal mass's average temperature] is ≥50° C. Operating this way,reverse-flow reactors can overcome certain difficulties encountered inthe operation of unidirectional-flow flow-through reactors for thespecified catalytic hydrocarbon conversion, e.g., the need foradditional cooling of the quench zone during the regeneration step ofunidirectional-flow reactors in continuous operation, e.g., additionalheat transfer away from the first portion of the thermal mass.

Certain aspects of the invention will now be described with respect to areverse-flow reactor having first and second heat-transfer zones and acatalytic hydrocarbon conversion zone, at least a portion of thecatalytic hydrocarbon conversion being located between the first andsecond heat-transfer zones. The invention is not limited to theseaspects, and this description is not meant to foreclose otherembodiments within the broader scope of the invention.

Referring now to FIG. 1A, a reverse flow reactor is provided, thereverse-flow reactor having first and second regions. The first regioncomprises a first heat transfer zone and a first portion of a catalytichydrocarbon conversion zone. The second region comprises a secondheat-transfer zone, and a second portion of the catalytic hydrocarbonconversion zone. The first heat transfer zone contains a first thermalmass M₁. The second heat transfer zone contains a second thermal massM₂. M₁ and M₂ can be selected from among the specified thermal masses,e.g., from thermal masses having the same composition and form as thosespecified in connection with the uni-flow flow-through reactor. M₁ andM₂ can be of substantially the same size, shape, density, and/orcomposition, but this is not required. The first and second thermalmasses are optionally parts (or portions) of a single monolith, e.g.,segments thereof.

The catalyst zone contains one or more of the specified catalytichydrocarbon conversion catalysts, C. As shown in the figure, portions ofthe hydrocarbon conversion catalyst are located in both the first andsecond catalytic hydrocarbon conversion zones, as indicated by theshading. For example, a first portion of the hydrocarbon conversioncatalyst can be located in the first portion of the catalytichydrocarbon conversion zone and a second portion of the hydrocarbonconversion catalyst can be located in the second portion of thecatalytic hydrocarbon conversion zone.

First and second feed mixtures are provided, as are first and secondutility fluids. The first and second feed mixtures are selected fromamong the specified feed mixtures. Optionally, the first and second feedmixtures have the same composition. Optionally, the first and secondfeed mixtures (or components thereof) are obtained from the same source.For example, the first feed mixture's first reactant can be of the samecomposition as the second feed mixture's first reactant, and both can beobtained from the same source, e.g., natural gas. The first feedmixture's oxidant can have the same composition as the second feedmixture's oxidant, and both can be obtained from the same source, e.g.,air. First and second utility fluids are also provided. The first andsecond utility fluids can be selected from among any of the specifiedutility fluids. The first and second utility fluids can have the samecomposition, and can be obtained from the same source, e.g., a steamgenerator.

At the start of the process, the first thermal mass M₁ is heated, e.g.,by exposing M₁ to a temperature in the range of from 550° C. to 1100° C.The hydrocarbon conversion catalyst C and the second thermal mass M₂ canbe at ambient temperature. At the start of a first time interval, a flowof the first feed mixture is established into the reverse-flow reactorvia its first aperture (not shown). The first feed mixture flows intopassages of M₁ via end 1 of M₁. Heat is transferred from M₁ to the firstfeed mixture in the first heat transfer zone (a pre-heat zone during thefirst interval) and the heated feed mixture transfers heat to at leastthe first portion of hydrocarbon conversion catalyst C (and optionallyto its second portion). At the start of the first interval, (i) theinitial average temperatures of M₁ and M₂, (ii) the initial averagetemperature of hydrocarbon conversion catalyst C, and (iii) the flowrate, temperature, and pressure of the first feed mixture arepre-determined to achieve:

-   -   A. an initial average temperature in at least the first portion        of the hydrocarbon conversion catalyst C in the range of from        550° C. to 1100° C. in the presence of the first feed mixture,        and    -   B. an initial average temperature of M₂ in the presence of a        first reactant mixture produced by the hydrocarbon conversion        reaction such that [the initial average temperature of the first        portion of the hydrocarbon conversion catalyst C−the initial        average temperature of M₂] is ≥50° C.

The hydrocarbon conversion reaction can be net endothermic or netexothermic, but is typically net exothermic. The first reaction mixtureis the same as that specified as resulting from operating a uni-flowflow-through reactor operating under substantially the same conditionsusing the specified first feed mixture.

The first reaction mixture flows through passages of M₂ and is quenchedin the second heat transfer zone (a quench zone during the first timeinterval) by a transfer of heat from the first reaction mixture to M₂. Afirst quenched reaction mixture is conducted away from end 2 of M₂, andout of the reverse-flow reactor via its second aperture (not shown).Olefin, e.g., C³⁻ olefin can be separated from the quenched firstreaction mixture downstream of the reverse-flow reactor. Olefinseparation can be carried out using one or more of the same methodsdescribed in connection with removing olefin from the specified reactionmixtures in uni-flow flow-through reactors.

FIG. 1A also schematically illustrates a temperature profile TP for thereverse-flow reactor during a net exothermic hydrocarbon conversionreaction carried out during the first time interval. Arrows on the TPcurve indicate a shift in the position of the peak in TP from upstreamto downstream as the first time interval progresses. As the peak in TPprogresses downstream, a time will be reached at which the averagetemperature of M₂ is <50° C. cooler than the average temperature of thesecond portion (the downstream portion) of the hydrocarbon conversioncatalyst. This is an indication that the first reaction mixture is notsufficiently quenched. The flow of first feed mixture is then lessenedor halted.

During a second time interval, illustrated in FIG. 1B, reverse flow isinitiated by passing the second feed mixture into the reverse-flowreactor through the second aperture (not shown) and into end 2 of M₂.Since M₂ is heated in the first interval, heat is transferred from M₂ tothe second feed mixture as the second feed mixture traverses theinternal passages of M₂. The heated second feed mixture conducted to theupstream portion (the second portion) of hydrocarbon conversion catalystC, where it is reacted to produce a second reaction mixture. The secondreaction mixture can have the same composition as the first reactionmixture.

The second reaction mixture is conveyed through the passages of M₁. Heatis transferred from the second reaction mixture to M₁, to produce aquenched second reaction mixture. The quenched second reaction mixtureis conducted out of end 1 of M₁, and then away from the reverse-flowreactor via the first aperture (not shown). The quenched second reactionmixture can be processed in the same way as is the first reactionmixture, e.g., for removal of C³⁻ olefin. The same equipment canprocesses can be used as is utilized for removing C³⁻ olefin from thequenched first reaction mixture.

The temperature profile TP during the second time interval is also shownin FIG. 1B. As indicated by arrows, the peak in TP shifts away from M₂toward M₁ during the second time interval. As the peak in TP progressesdownstream, a time will be reached at which the average temperature ofM₁ is <50° C. cooler than the average temperature of the first portion(the downstream portion) of the hydrocarbon conversion catalyst. This isan indication that the second reaction mixture is not sufficientlyquenched. The flow of second feed mixture is then lessened or halted.

The first and second time intervals can be substantially non-overlappingintervals. Each of the first and second time intervals can be,independently, an interval having a duration in the range of from about0.5 seconds to about 15 seconds. The interval between the first andsecond time intervals (the “dead-time”, which represents the interval oftime it takes to reverse flow of the feed mixtures) is preferably asshort as possible so that the reverse flow cycle can be as rapid aspossible. From a practical standpoint, the dead-time should be, e.g.,≤than 0.5 seconds, such as in a range of from about 0.01 seconds toabout 0.5 seconds. Upon completion of the second time interval, theintervals can be repeated. That is, the flow shown in FIG. 1A can bereinitiated and followed by subsequent reinitiation of the flow shown inFIG. 1B. When operated in a reverse-flow reactor, the process's cycletime is generally ≥0.5 second, such as in the range of 10 seconds to 240seconds, in the range of 10 seconds to 120 seconds, in the range of 20seconds to 60 seconds, or in the range of 20 seconds to 40 seconds. Theterm “cycle time” means the time from a first time interval to the nextfirst time interval, including (i) any intervening time intervals (e.g.,second, third, and/or fourth intervals) and (ii) any dead-time betweenany pair of intervals.

In certain aspects, at least a portion of the hydrocarbon conversioncatalyst is located in a region of the reverse-flow reactor that isbetween the first and second thermal masses. For example, ≥50.0 wt. % ofthe hydrocarbon conversion catalyst, based on total weight of thehydrocarbon conversion catalyst, can be located in a zone between thefirst and second regions. The first and second regions can be separate,non-overlapping regions of the reverse-flow reactor. In other aspects,at least part of the hydrocarbon conversion catalyst is located on or inthe passages of M₁ and/or M₂. For example, (i) ≥50% (weight basis) ofthe first portion of the hydrocarbon conversion catalyst can be locatedin the passages of M₁ and (ii) ≥50% (weight basis) of the second portionof the hydrocarbon conversion catalyst can be located in the passages ofM₂.

A portion of M₁ can be located outside the first heat transfer zoneand/or a portion of M₂ can be located outside the second heat transferzone. In certain aspects, (i) ≥50.0% of M₁ is located in the firstheat-transfer zone, with any remaining portion located in that part ofcatalytic hydrocarbon conversion zone that is proximate to M₁, and (ii)≥50.0% of M₂ is located in the second heat-transfer zone, with anyremaining portion located in that part of catalytic hydrocarbonconversion zone that is proximate to M₂.

Optionally, the reverse-flow reactor comprises first and secondsorbents. The first and second sorbents can be one or more of thosesorbents specified in connection with a uni-flow flow-through reactor.The first and second sorbents typically have the same composition.Certain aspects utilizing first and second thermal masses and first andsecond sorbents are illustrated schematically in FIGS. 2A and 2B. Theinvention is not limited to these aspects, and this description is notmeant to foreclose other aspects within the broader scope of theinvention.

As shown in FIGS. 2A and 2B, the first and second thermal masses M₁ andM₂ are monolithic honeycombs (e.g., of refractory such as ceramic)having internal passages for the flow of first and second feed mixturesand first and second reactants as the case may be. M₁ and M₂ can beselected from among the specified thermal masses, e.g., from thermalmasses having the same composition and form as those specified inconnection with a uni-flow flow-through reactor. First sorbent A₁ islocated proximate to M₁, and is in the form of a honeycomb monolithcomprising internal passages, the internal passages containing at leasta portion of the first sorbent, which is exposed to the flow of thefirst feed mixture, the second reactant mixture, a second raffinate, andat least a second utility fluid. Second sorbent A₂ is located proximateto M₂, and is in the form of a ceramic honeycomb monolith comprisinginternal passages, the internal passages containing at least a portionof the second sorbent, which is exposed to the flow of the second feedmixture, the first reactant mixture, a first raffinate, and at least afirst utility fluid. A₁ and A₂ can be selected from among the specifiedsorbents, e.g., from sorbents having the same composition and form asthose specified in connection with a uni-flow flow-through reactor. Thefirst and second sorbents are typically selective for sorbing C₂hydrocarbon, e.g., for sorbing ethylene, under kinetic sorptionconditions.

In the aspects illustrated in FIGS. 2A and 2B, the reverse-flow reactorfurther comprises at least one hydrocarbon conversion catalyst. Thehydrocarbon conversion catalyst is located within passages of ahoneycomb monolith C, e.g., in the form of one or more of the specifiedcatalysts as particles and/or layer(s) on the internal surfaces ofpassages within monolith C. Catalyst monolith C is located betweenthermal mass monoliths M₁ and M₂. Thermal mass monolith M₁ is locatedbetween sorbent monolith A₁ and catalyst monolith C. Thermal massmonolith M₂ is located between sorbent monolith A₂ and catalyst monolithC. A₁, M₁, and 50% of C are located in a first region of thereverse-flow reactor. A₂, M₂, and the remaining 50% of C are located ina second region of the reverse-flow reactor. The reverse-flow reactor'scatalytic hydrocarbon conversion zone includes C. The reverse-flowreactor's first sorption zone includes A₁, and the second sorption zoneincludes A₂. The reverse-flow reactor's first heat transfer zoneincludes M₁, and the second heat transfer zone includes M₂. Except forheat transfer to/from the catalytic hydrocarbon conversion zone andto/from the first and second sorption zones, the zones are substantiallynon-overlapping.

At the start of the process, first sorbent A₁ and first thermal mass M₁are heated, e.g., by exposing them to a temperature in the range of from550° C. to 1100° C. The hydrocarbon conversion catalyst C, the secondthermal mass M₂, and second sorbent A₂ can be at ambient temperature. Atthe start of a first time interval, a flow of the first feed mixture isestablished into the reverse-flow reactor via its first aperture (notshown). The first feed mixture flows into passages of A₁ via end 1, andtransits the internal passages of A₁ and M₁. Heat is transferred from tothe first feed mixture to M₁ and optionally A₁ in the first heattransfer zone (a pre-heat zone during the first interval). The heatedfirst feed mixture transfers heat to the hydrocarbon conversion catalystC in the catalytic hydrocarbon conversion zone. At the start of thefirst interval (ii) the initial average temperature of hydrocarbonconversion catalyst C, (ii) the flow rate, temperature, and pressure ofthe first feed mixture, and (iii) the initial average temperatures ofM₁, M₂, A₁, and A₂ are pre-determined to achieve:

-   -   A. an initial average temperature of hydrocarbon conversion        catalyst C in the range of from 550° C. to 1100° C. in the        presence of the first feed mixture,    -   B. an initial average temperature of M₂ in the presence of a        first reactant mixture produced by the hydrocarbon conversion        reaction such that [the initial average temperature of the first        portion of the hydrocarbon conversion catalyst C−the initial        average temperature of M₂] is ≥50° C., and    -   C. an initial average temperature of A₂ such that [the initial        average temperature of M₂−the initial average temperature of A₂]        is ≥50° C.

The hydrocarbon conversion reaction can be net endothermic or netexothermic, but is typically net exothermic. The first reaction mixtureis the same as that specified as resulting from operating a uni-flowflow-through reactor operating under substantially the same conditionsusing the specified first feed mixture.

The first reaction mixture flows through passages of M₂ and is quenchedin the second heat transfer zone (a quench zone during the first timeinterval) by a transfer of heat from the first reaction mixture to M₂. Afirst quenched reaction mixture is conducted away from M₂, and thenthrough the internal passages of A₂. At least a portion of the C₂hydrocarbon is sorbed from the quenched first reaction mixture in A₂. Afirst raffinate (depleted in C₂ hydrocarbon) is conducted away from A₂via end 1. The first raffinate can be conducted away from thereverse-flow reactor via its second aperture (not shown), e.g., forremoving from the raffinate at least a portion of any remainingadditional C₂ hydrocarbon. During the first time interval, the peak inthe reverse-flow reactor's temperature profile TP (not shown) shiftsaway from A₁ and M₁ toward M₂ and A₂.

Within a predetermined time before, at, or after break-through of thedesired sorbate from A₂, the passing of the first reaction mixture tothe reverse-flow reactor can be lessened or discontinued, in order todesorb sorbate from A₂. This can be carried out during a second timeinterval as shown in FIG. 2B.

During the second time interval, a first utility fluid is conducted intothe reverse-flow reactor's first aperture (not shown). The utility fluidtransits the internal passages of A₁ and M₁, optionally absorbing heatfrom those monoliths to further cool them. The utility fluid thentransits the internal passages of monolith C, and absorbs heat in thereverse-flow reactor's catalytic hydrocarbon conversion zone to cool thehydrocarbon conversion catalyst. Additional heat is transferred to theutility fluid as it transits the internal passages of M₂, which coolsM₂. Heat is transferred from the heated utility fluid to A₂ in order todesorb the sorbate. In other words, the flow of first utility fluidfurther displaces the peak of temperature profile TP away from M₂ towardA₂. The flow of first utility fluid is typically maintained until theamount of the desired sorbate in the first utility fluid is less than apre-determined amount, after which the desorption can be halted.Desorption conditions can be the same as those specified for use inconnection with uni-flow flow-through reactors. Typically, desorption iscarried out under kinetic desorption conditions. C₂ hydrocarbon can beremoved from the rich first utility fluid by conventional methods, butthe invention is not limited thereto.

Following desorption, the flow of first utility fluid is lessened orsubstantially halted. A second feed mixture is then introduced into thereverse-flow reactor in an average flow direction that is opposite tothe average flow direction during the first and second time intervals.When the reverse-flow reactor is physically symmetric about an imaginaryline separating the first and second regions, as shown in FIGS. 2A and2B, and the second feed mixture is substantially the same as the firstfeed mixture, the second reaction mixture is processed to produce asecond raffinate having substantially the same composition as the firstraffinate. In other words, the reactor can be operated the same way asduring the first time interval, but in the reverse direction. A secondutility fluid can be utilized for desorbing the desired sorbate from A₁,and for restoring A2, M₂, C, M₁, and A₁ to conditions suitable forre-introducing the first feed mixture into the reverse-flow reactor'sfirst aperture.

The time intervals during which (i) catalytic conversion of reactant andoxidant is carried out in the forward direction, (ii) desorption iscarried out in the forward direction, (iii) catalytic reaction ofreactant and oxidant is carried out in the reverse direction, and (iv)desorption is carried out in the reverse direction, e.g., the first,third, second, and fourth time intervals, can be non-overlapping timeintervals. The process can be carried out repetitively, if desired,e.g., by repeating a cycle of first time interval, third time intervalsecond time interval, and fourth time interval. Dead-time betweenadjacent time intervals is generally ≤0.5 seconds, e.g., ≤0.25 seconds.In the aspects illustrated in FIGS. 2A and 2B, the process's cycle timeis generally ≥0.5 second, such as in the range of 10 seconds to 240seconds, in the range of 10 seconds to 120 seconds, in the range of 20seconds to 60 seconds, or in the range of 20 seconds to 40 seconds.Relatively longer cycle times are typically encountered over those ofaspects illustrated in FIGS. 1A and 1B, as a result of the desirabilityof desorbing C₂ sorbate from sorbent located in the reverse-flow reactor(e.g., A₁ and A₂).

In the present disclosure, a reactor refers to equipment used forchemical conversion. As such, several items identified as reactors maybe combined to become a single entity that is also identified as areactor, in that individual and combined entities may be characterizedas equipment used for chemical conversion. Accordingly, a plurality ofreverse flow reactors can be utilized together, e.g., in series,parallel, and/or series-parallel. For example, a system of tworeverse-flow reactors can be operated in series. In a first step, afirst feed mixture is passed to a first stage of a reactor that includesa heated first thermal mass and a second thermal mass. The first feedmixture can be heated with the heated first thermal mass, and the heatedfirst feed mixture can be contacted in the first stage with a firsthydrocarbon conversion catalyst to convert at least a portion of thealkane to alkene, producing an alkene-containing first stage reactionmixture. The first reaction mixture is then quenched by transferringheat from the first reaction mixture to the second thermal mass. Atleast a portion of the alkene can be separated from the quenched firststage reaction mixture to produce first stage raffinate comprisingwater, any remaining alkene, and unconverted alkane from the first stagereaction mixture. The first stage raffinate can be transferred to asecond stage of the reactor, with the second stage including third andfourth thermal masses, the third thermal mass being a heated thermalmass at the start of transfer of the first stage raffinate to the secondstage of the reactor. The first stage raffinate can be heated with theheated third thermal mass; and the heated first stage raffinate can becontacted in the second stage with a second hydrocarbon conversioncatalyst to convert at least a portion of the unconverted alkane in thefirst stage raffinate to alkene, producing an alkene-containing secondstage reaction mixture. The second stage reaction mixture is thenquenched by the fourth thermal mass by transferring heat from the secondstage reaction mixture to the fourth thermal mass. At least a portion ofthe alkene can be removed from the quenched second stage reactionmixture to produce a second stage raffinate. Flowing the first feedmixture to the reactor can then be lessened or discontinued. A secondfeed mixture, which can be of the same composition as the first feedmixture, is then passed to the series reactor system in an average flowdirection that is opposite to the first feed mixture's average flowdirection.

EXAMPLE

An example of a reverse-flow reactor system utilized for the specifiedcatalytic hydrocarbon conversion is depicted in FIGS. 3-5. The reactorcomprises two reactor stages 102 and 104. The first reactor stage 102comprises Zones 1-3. Zone 1 in includes first heat transfer and firstsorption functionalities. Zone 2 includes catalytic hydrocarbonconversion functionality. Zone 3 includes second heat transfer andsecond sorption functionalities. The second reactor also includes threezones. Zone 4 in includes first heat transfer and first sorptionfunctionalities. Zone 5 includes catalytic hydrocarbon conversionfunctionality. Zone 6 includes second heat transfer and second sorptionfunctionalities. Zones 1 and 4 each include (i) a first thermal massselected from among the specified thermal masses and (ii) a firstsorbent selected from among the specified sorbents. Zones 2 and 5 eachinclude at least one of the specified hydrocarbon conversion catalysts.Zones 3 and 6 each include (i) a second thermal mass selected from amongthe specified thermal masses and (ii) a second sorbent selected fromamong the specified sorbents.

It is understood that one or more valves and other flow control devices(e.g., check valves, louvers, flow restrictors, timing systems, etc.)can be used to control fluid flow through reactor stages 102 and 104,which include first and second feed mixtures, and an optional utilityfluid (e.g., a gas such as sweep gas). For example, a means forconveying fuel, oxidant, reactant, alkane feed mixture, and/or utilityfluid (e.g., via conduits 110, 112, 114, 116, 118, and 120) into theappropriate passages in the first and second reactor stages may includeone or more of plenums, valves, vanes, spargers, and/or distributors.Suitable spargers, distributors, etc., are disclosed in U.S. Pat. No.7,815,873, which is incorporated by reference herein in its entirety.Although the invention is compatible with conventional spargers,distributors, plenums, etc., it is not limited thereto, and thisdescription is not meant to foreclose other flow-control means withinthe broader scope of the invention.

The specified hydrocarbon conversion reaction progresses from the firststage 102 to the second stage 104. At the start of a first timeinterval, illustrated in FIG. 3, Zones 1-3 and Zones 4-6 are atsubstantially the same conditions specified for the first step of theaspects illustrated in FIGS. 2A and 2B. During the first time interval,a first reactant selected from among one of the feed mixture's specifiedreactants is conducted through conduit 110 to first distributor 122A,which directs the flow of the first reactant into the first reactorstage 102. A first oxidant (e.g., oxygen, such as oxygen obtained fromair or oxygen in air) is conducted separately via conduit 112 into thefirst reactor stage 102. The first reactant and oxidant flow throughpassages of the first thermal mass and first sorbent, in comparable flowas previously described with regard to FIG. 2A. The first reactant andthe first oxidant can be combined to produce the first feed mixtureupstream of Zone 1. In other aspects, the first reactant and firstoxidant are conveyed through separate channels of the first thermalmass, with the heated first reactant and heated first oxidant then beingcombined to produce a heated first feed mixture upstream of Zone 2. Instill other aspects, one component of the first feed mixture, e.g., oneof diluent, first reactant, or first oxidant, is conducted through theat least one channel of the first thermal mass (for heating thatcomponent and cooling the first thermal mass. The other first feedmixture component(s) are conducted, e.g., via a conduit external to thereverse-flow reactor, to a location upstream of Zone 2, where thesecomponents are introduced into the first stage reactor 102. The firstfeed mixture's reactant and oxidant can be combined downstream of Zone 1but upstream of Zone 2 to produce the heated first feed mixture. So longas (i) sufficient heat is provided to the first feed mixture from thefirst thermal mass to accomplish the specified catalytic reaction inzone 2, it is not necessary for both the first reactant and the firstoxidant to pass through the passages of the first thermal mass. Theheated first feed mixture is then conducted to Zone 2.

In aspects illustrated in FIG. 3, the passages of the reactor Zone 2contain at least one of the specified hydrocarbon conversion catalysts,for converting at least a portion of the heated first feed mixture'salkane to C₂₊ olefin. The C₂₊ olefin is a component of a first-stagereaction mixture produced in Zone 2, the first-stage reaction mixturefurther comprising at least a portion of any by-products of the reaction(e.g., water), at least a portion of any unconverted first feed mixtureor components thereof, and at least a portion of any unreacted diluent(e.g., unreacted nitrogen when the oxidant is molecular oxygen in air).Heat is transferred from the first-stage reaction mixture to the secondthermal mass in Zone 3 to produce a quenched first stage reactionmixture.

A temperature profile TP is shown along first reactor stage 102 in FIG.3. When a net exothermic catalytic hydrocarbon conversion reaction iscarried out in Zone 2, the peak of temperature profile TP exhibits anincreasing temperature. TP then exhibits a decreasing temperature asheat is transferred from the flowing first-stage reaction mixture to thesecond thermal mass during quenching. As shown by the arrow, the peak inTP moves away from Zone 1 toward Zone 3 during the first time interval.At least a portion of the quenched first-stage reaction mixture's olefinis sorbed by the first sorbent as the quenched second-stage reactionmixture transits Zone 3.

A quenched first-stage reaction mixture depleted in olefin (afirst-stage raffinate) is passed to second stage 104 via conduit 116 toa sparger 108A. The first-stage raffinate comprises unconverted alkane,and at least a portion of any (i) unconverted oxidant and/or (ii)unreacted any unreacted diluent (e.g., unreacted nitrogen, when theoxidant is molecular oxygen in air). If needed to maintain thealkane:oxidant molar ratio in the specified range, additional oxidant(e.g., oxygen in air or obtained from air) can be conducted via conduit118 into the second reactor stage 104 for combining with the first-stageraffinate in second reactor 104.

The first-stage raffinate and additional oxidant flow through a firstheated thermal mass, analogous to the first thermal mass of Region 1 inFIG. 2A. Heat is transferred from the heated first thermal mass to thefirst-stage raffinate as the raffinate transits Zone 4. At least aportion of the additional oxidant is added to the heated first-stageraffinate upstream of Zone 5. Zone 5 contains passages which include atleast one of the specified hydrocarbon conversion catalysts, forconverting unconverted alkane in the first-stage raffinate to asecond-stage reaction mixture comprising C₂₊ olefin produced in Zone 5,at least a portion of (i) any reaction by-products (e.g., water), (ii)any unconverted additional oxidant, and (iii) any unconvertedfirst-stage raffinate or components thereof (including any C₂₊ olefinfrom the first-stage raffinate). When the hydrocarbon conversionreaction of Zone 5 is net exothermic, the peak in TP moves in thedirection of Zone 6, as shown in the temperature profile along reactorstage 104.

As the second-stage reaction mixture pass away from reaction Zone 5, itscomponents are further mixed and passed through the second thermal massof second reactor 104, located in Zone 6. Heat is transferred to thesecond thermal mass from the second-stage reaction mixture in Zone 6 toproduce a quenched second-stage reaction mixture. At least a portion ofthe quenched second-stage reaction mixture's olefin is sorbed by thesecond sorbent of second reactor 104, located in Zone 6. A second-stageraffinate (the quenched, olefin-depleted, second-stage reaction mixture)exits the second reactor stage 104 through the conduit 120. Thesecond-stage raffinate typically comprises unreacted by-products of thecatalytic hydrocarbon conversion of Zones 2 and/or 5, e.g., water. Thesecond-stage raffinate typically further comprises at least a portion of(i) any unconverted first mixture or components thereof, (ii) anyunconverted diluent (e.g., unconverted nitrogen when the oxidant and/oradditional oxidant is molecular oxygen in air, and (iii) any unconvertedadditional oxidant.

After a first time interval, the flow of first reactant and firstoxidant to reactor stage 102 are stopped (as in any additional oxidant,provided to reactor 104). During a second time interval, the sorbedolefins (sorbate) of Zones 3 and 6 are desorbed. During the third timeinterval, a heated utility fluid, which can be selected from among anyof the specified utility fluids, e.g., steam, is flowed through thereactor 102 and/or reactor 104. Heat is transferred from the heatedutility fluid to the sorbents of Zone 3 and/or Zone 4, to release (e.g.,desorb) olefin. The cooled utility fluid is utilized as a sweep gas,e.g., as a moving force to remove the olefin remaining in the reactor.Besides steam, utility fluid can be selected from among one or more ofnitrogen, substantially inert gas such as argon, etc. When the utilityfluid is steam, conventional methods can be utilized to (i) condense thesteam and (ii) to separate desorbed olefin from the condensed steam.

As shown in FIG. 4, steam is utilized as the heated utility fluid. Thesteam is conducted through conduits 110 and 116 of first and secondreactor stages 102, 104, respectively. As the utility fluid passesthrough the reactor stages, the high temperature region of thetemperature profiles for reactors 102 and 104 decrease in peaktemperature and shifts downstream (with respect to utility fluid flow)as indicated by profiles TP alongside each reactor stage. For example,as the steam is flowed through the reactor stages, the portion ofthermal masses located in Zones 3 and 6 are eventually heated to atemperature in the range of from 200° C. to 600° C., e.g., about 400° C.At a temperature in this range, the sorbent of Zones 3 and 6 is lessselective to the desired sorbate, e.g., C₂ hydrocarbon, such asethylene. This means that as the temperature in the sorbent zonesincreases, sorbate can be readily desorbed and removed via conduits 114and 120. Following desorption, the flow of steam is lessened orsubstantially halted. If needed, a combustion interval can be utilizedfor restoring the temperatures of thermal masses located in regions 1-6before the flow of reactants is provided in the reverse direction (forthe second time interval). Typically, utility fluid flow (and sorbatedesorption) is substantially halted before ≥10% of the area under curveTP is downstream of Zones 3 or 6. In those aspects, little or nocombustion is needed for reactor pre-heating. This represents a balancebetween advantageously desorbing more olefin and disadvantageouslylosing heat from the reactor. Kinetic sorption and desorption conditionsare typically used, and the durations of the process's cycle times aretypically selected accordingly.

Since the reverse-flow reactors of FIGS. 3 and 4 are substantiallysymmetric, the reaction can be carried out in reverse-flow mode undersubstantially the same conditions. FIG. 5 depicts an example of reverseflow relative to the flow shown in FIG. 3. Reverse flow is carried outin a third time interval following the second time interval. As shown inFIG. 5, a second reactant, which can be selected from among any of thereactants specified for use as a first reactant, is conducted throughsparger 108B of reactor 104. A second oxidant, which can be selectedfrom among any of the oxidants specified for use as a first oxidant, isconducted into reactor 104 through conduit 120. The second reactant canbe of the same composition as the first reactant, and the second oxidantcan be of the same composition as the first oxidant, but this is notrequired.

The second reactant and second oxidant flow through separate passages orchannels of the heated second thermal mass (heated by the utility fluidduring the desorption) located in Zone 6. For example, the secondreactant can flow through the second thermal mass via a reactant passageor reactant channel(s), and the second oxidant can flow through thesecond thermal mass via an oxidant passage or oxidant channel(s). Thereactant and oxidant streams are heated and mixed together priorentering reactor Zone 5, forming a second feed mixture analogous to thesecond feed mixture of the aspects illustrated in FIG. 1B. Except forflow direction, the flow conditions, reactor temperature profiles,reactant, oxidant, reaction products, etc., in reverse-flow (second timeinterval as shown in FIG. 5) can be substantially the same as those ofthe first time interval (as shown in FIG. 3).

When an exothermic the hydrocarbon conversion reaction is carried out inZone 5, the peak of TP for reverse-flow reactors 102 and 104 moves inthe direction of Zones 1 and 4. The temperature decreases in Zones 6,resulting from the transfer of heat from the second thermal mass to thesecond reactant and/or second oxidant. The temperature of the TPincreases in Zone 4, as a result of heat transfer to the first thermalmass from the first-stage reaction mixture. As is clear from the figure,when operating in reverse-flow the first stage is reactor 104 and thesecond stage is reactor 102. This heat transfer produces a quenchedfirst-stage reaction product. At least a portion of the first-stagereaction mixture's olefin is removed in Zone 4 by the first sorbent.

A first-stage raffinate is passed to second stage 102 via sparger 122B.The first raffinate (and second stage reaction mixture) flow throughZones 1-3, is in reverse flow with regard to FIG. 3. Additional oxidantcan be added, if needed to maintain the specified alkane:oxidant molarratio, via sparger 114. The additional oxidant can be substantially thesame as that utilized in the aspects shown in FIG. 3, in substantiallythe same amount.

Heat is transferred to the first-stage raffinate from the second thermalmass of reactor 102. The heated first-stage raffinate is passed throughdistribution means (e.g., one or more mixer/distributors) prior enteringZone 2, for converting at least a portion of the heated first-stageraffinate's alkane and at least a portion of (i) any oxidant in thefirst-stage raffinate and (ii) any additional oxidant in the presence ofthe hydrocarbon conversion catalyst located in reactor 102 to produce asecond-stage reaction mixture comprising C₂₊ olefin. Heat is transferredfrom the second-stage reaction mixture to the first thermal mass locatedin Zone 1 to produce a quenched second-stage reaction mixture. As seenin a temperature profile TP along reactor stage 102, when an exothermicthe hydrocarbon conversion reaction is carried out in the Zone 2, thepeak of TP moves toward zone 1.

At least a portion of the second-stage reaction mixture's C₂₊ olefin isselectively removed by the first sorbent of reactor 102, located inZone 1. A second-stage raffinate is conducted away from Zone 1 viaconduit 112. A desorption time interval (e.g., a fourth time interval)can be utilized for desorbing at least a portion of the olefin sorbed inZones 1 and 4. The desorption can be substantially the same as thatillustrated in FIG. 4, but with the flow of steam in the reversedirection. When (i) reactors 102 and 104 are substantially identical andcontain substantially identical components, (ii) when the first feedmixture has substantially the same composition as the second feedmixture, and (iii) when substantially the same process conditions(temperature, pressure, flow rate) subsist in the first and secondstages in forward-flow-mode and in reverse-flow mode, then (iv) thecomposition of the second-stage raffinate in forward-flow mode will besubstantially the same as that is reverse-flow mode and the desorbed C₂₊olefin stream desorbed in forward-flow mode is substantially the same asthat desorbed in reverse-flow mode.

By utilizing a system comprising a plurality of catalytic, regenerative,reverse-flow reactors in series, the amount of unconverted alkane in theraffinate exiting the most downstream reactor can be reduced to very lowamounts, e.g., less than 1% (by weight) of the raffinate, such as lessthan 1%. Accordingly, the low conversion of the prior art methods isovercome, without the need for recycling unconverted alkane to anupstream reactor in the system.

While the present invention has been described and illustrated withrespect to certain embodiments or aspects, it is to be understood thatthe invention is not limited to the particulars disclosed and extends toall equivalents within the scope of the claims. Unless otherwise stated,all percentages, parts, ratios, etc. are by weight. Unless otherwisestated, a reference to a compound or component includes the compound orcomponent by itself as well as in combination with other elements,compounds, or components, such as mixtures of compounds. Further, whenan amount, concentration, or other value or parameter is given as a listof upper preferable values and lower preferable values, this is to beunderstood as specifically disclosing all ranges formed from any pair ofan upper preferred value and a lower preferred value, regardless ofwhether ranges are separately disclosed. All patents, test procedures,and other documents cited herein, including priority documents, arefully incorporated by reference to the extent such disclosure is notinconsistent and for all jurisdictions in which such incorporation ispermitted.

The invention claimed is:
 1. A reverse-flow reactor, comprising: firstand second thermal masses, each having first and second portions, thefirst and second portions together comprising ≥99.0 wt. % of the firstor second thermal mass as the case may be, wherein the first and secondthermal masses each include one or more passages adapted for fluid flow;first, second, third, fourth, and fifth regions, wherein (i) the firstand second regions are adjacent, non-overlapping regions, (ii) the thirdand fourth regions are adjacent, non-overlapping regions, (iii) thefirst region contains the first portion of the first thermal mass andthe second region contains the second portion of the first thermal mass,(iv) the third region contains the first portion of the second thermalmass and the fourth region contains the second portion of the secondthermal mass, (v) the fifth region is a non-overlapping region locatedbetween the second and third regions, and (vi) the fifth region isadapted for fluid communication between the first and second thermalmasses and optionally for fluid mixing; at least one first reaction zonelocated in the second region, at least one of the reaction zonescontaining at least one hydrocarbon conversion catalyst, the catalystbeing (i) at least one hydrogen transfer catalyst and/or at least onefirst oxydehydrogenation catalyst, and the hydrocarbon conversioncatalyst being in fluid communication with the passages of the firstthermal mass; at least one first sorbent zone in the first region, thefirst sorbent zone containing at least one olefin-selective sorbent thatis in fluid communication with the passages of the first thermal mass;at least one second reaction zone located in the third region, at leastone of the reaction zones containing at least one secondoxydehydrogenation catalyst that is in fluid communication with thepassages of the second thermal mass; and at least one second sorbentzone in the fourth region, the second sorbent zone containing at leastone olefin-selective sorbent that is in fluid communication with thesecond thermal mass.
 2. A flow-through reactor for producing olefin,comprising: (a) a reactor vessel configured for fluid-flow; (b) at leastone hydrocarbon conversion catalyst located within the reactor vessel,the hydrocarbon conversion catalyst being configured for contact withthe fluid-flow and including (i) at least one oxidative couplingcatalyst and/or (ii) at least one oxydehydrogenation catalyst; (c) atleast one sorbent located in the reactor vessel, the sorbent beingselective for olefin sorption and configured for contact with thefluid-flow; and (d) at least one thermal mass located in the reactorvessel, the thermal mass being configured for contact with thefluid-flow, and at least a portion of the fluid-flow contacting part ofthe thermal mass being located between the hydrocarbon conversioncatalyst and the sorbent.
 3. The reverse-flow reactor of claim 1, inwhich the olefin-selective sorbent is a copper salt-treated zeolite 4A,a copper salt-treated zeolite X, a copper salt-treated zeolite Y, acopper salt-treated alumina, or a copper salt-treated silica.
 4. Thereverse-flow reactor of claim 1, in which the olefin-selective sorbentis a clay sorbent impregnated with silver ion.
 5. The flow-throughreactor of claim 2, in which the olefin-selective sorbent is a coppersalt-treated zeolite 4A, a copper salt-treated zeolite X, a coppersalt-treated zeolite Y, a copper salt-treated alumina, or a coppersalt-treated silica.
 6. The flow-through reactor of claim 2, in whichthe olefin-selective sorbent is a clay sorbent impregnated with silverion.
 7. The reverse-flow reactor of claim 1, in which theolefin-selective sorbent comprises a copper compound or a silvercompound supported on silica, a copper compound or a silver compoundsupported on alumina, a copper compound or a silver compound supportedon MCM-41 zeolite, a copper compound or a silver compound supported on4A zeolite, a copper compound or a silver compound supported on a carbonmolecular sieve, or a copper or silver compound supported on a polymerresin.
 8. The reverse-flow reactor of claim 2, in which theolefin-selective sorbent comprises a copper compound or a silvercompound supported on silica, a copper compound or a silver compoundsupported on alumina, a copper compound or a silver compound supportedon MCM-41 zeolite, a copper compound or a silver compound supported on4A zeolite, a copper compound or a silver compound supported on a carbonmolecular sieve, or a copper or silver compound supported on a polymerresin.
 9. The reverse-flow reactor of claim 1, in which theolefin-selective sorbent comprises a Faujasite zeolite.
 10. Thereverse-flow reactor of claim 2, in which the olefin-selective sorbentcomprises a Faujasite zeolite.
 11. The reverse-flow reactor of claim 1,in which the olefin-selective sorbent comprises a metal-organicframework, an iron-organic framework or a metal-organic framework havingat least one redox-active metal center.
 12. The reverse-flow reactor ofclaim 2, in which the olefin-selective sorbent comprises a metal-organicframework, an iron-organic framework or a metal-organic framework havingat least one redox-active metal center.
 13. The reverse-flow reactor ofclaim 1, in which the olefin-selective sorbent comprises analuminophosphate.
 14. The reverse-flow reactor of claim 2, in which theolefin-selective sorbent comprises an aluminophosphate.